Consultation Paper

Expert Evidence









(LRC CP 52-2008)


© Copyright

Law Reform Commission



December 2008


ISSN 1393-3140




The Law Reform Commission is an independent statutory body established by the Law Reform Commission Act 1975. The Commission’s principal role is to keep the law under review and to make proposals for reform, in particular by recommending the enactment of legislation to clarify and modernize the law. Since it was established, the Commission has published over 140 documents containing proposals for law reform and these are all available at Most of these proposals have led to reforming legislation.


The Commission’s role is carried out primarily under a Programme of Law Reform. Its Third Programme of Law Reform 2008-2014 was prepared by the Commission following broad consultation and discussion. In accordance with the 1975 Act, it was approved by the Government in December 2007 and placed before both Houses of the Oireachtas. The Commission also works on specific matters referred to it by the Attorney General under the 1975 Act. Since 2006, the Commission’s role includes two other areas of activity, Statute Law Restatement and the Legislation Directory.


Statute Law Restatement involves the administrative consolidation of all amendments to an Act into a single text, making legislation more accessible. Under the Statute Law (Restatement) Act 2002, where this text is certified by the Attorney General it can be relied on as evidence of the law in question. The Legislation Directory - previously called the Chronological Tables of the Statutes - is a searchable annotated guide to legislative changes. After the Commission took over responsibility for this important resource, it decided to change the name to Legislation Directory to indicate its function more clearly.


The Law Reform Commission consists of a President, one full-time Commissioner and three part-time Commissioners.


The Commissioners at present are:



The Hon Mrs Justice Catherine McGuinness

Former Judge of the Supreme Court


Full-time Commissioner:

Patricia T. Rickard-Clarke, Solicitor


Part-time Commissioner:

Professor Finbarr McAuley


Part-time Commissioner:

Marian Shanley, Solicitor


Part-time Commissioner:

Donal O’Donnell, Senior Counsel


Law Reform Research Staff

Director of Research:

Raymond Byrne BCL, LLM (NUI),



Legal Researchers:

Chris Campbell B Corp, LLB Diop Sa Gh (NUI)

Frances Colclough BCL, LLM (NUI)

Siobhan Drislane BCL, LLM (NUI)

Claire Murray, BCL (NUI), Barrister-at-Law

Gemma Ní Chaoimh BCL, LLM (NUI)

Bríd Nic Suibhne BA, LLB, LLM (TCD), Diop sa Gh (NUI)

Jane O’Grady BCL, LLB (NUI ), LPC (College of Law)

Gerard Sadlier BCL (NUI)

Joseph Spooner, BCL (Law with French Law) (NUI), Dip. French and European Law (Paris II), BCL (Oxon)

Ciara Staunton BCL, LLM (NUI), Diop sa Gh (NUI)


Statute Law Restatement

Project Manager for Restatement:

Alma Clissmann, BA (Mod), LLB, Dip Eur Law (Bruges), Solicitor


Legal Researchers:

John P Byrne BCL, LLM (NUI), Barrister-at-Law

Elizabeth Fitzgerald LLB, M.Sc. (Criminology & Criminal Justice), Barrister-at-Law

Catriona Moloney BCL (NUI), LLM (Public Law)


Legislation Directory

Project Manager for Legislation Directory:

Heather Mahon LLB (ling. Ger.), M.Litt, Barrister-at-Law


Legal Researchers:

Margaret Devaney LLB, LLM (TCD)

Rachel Kemp BCL (Law and German), LLM (NUI)


Administration Staff

Executive Officers:

Deirdre Bell

Simon Fallon

Darina Moran

Peter Trainor


Legal Information Manager:

Conor Kennedy BA, H Dip LIS



Eithne Boland BA (Hons), H Dip Ed, H Dip LIS


Clerical Officers:

Ann Browne

Ann Byrne

Liam Dargan

Sabrina Kelly


Principal legal researcher for this CONSULTATION PAPER

Margaret Maguire LLB, LLM (NUI)


Further information can be obtained from:


The Law Reform Commission

35-39 Shelbourne Road


Dublin 4



+353 1 637 7600



+353 1 637 7601







The Commission would like to thank the following people who provided valuable assistance in the preparation of this Consultation Paper:


Association of Consulting Forensic Engineers

Ms. Caroline Conroy, Managing Director, La Touche Witness Training, Ireland

Ms. Penny Cooper, Director of Continuing Professional Development and Witness Preparation Training, City Law School, City University, London

Dr. Chris Pamplin, UK Register of Expert Witnesses

Mr. Ciaran Fahy, Consulting Engineer

Mr. Andrew Burr, Barrister-at-Law, Atkin Chambers, London

Mr. Paul Romeril, Consulting Engineer



Full responsibility for this publication lies, however, with the Commission.


Table of Cases                                                                                       xiii

Introduction  1

A     Background to the project 1

B     The admissibility of expert evidence of opinion and         the role of the expert witness in court 1

C     The challenges involved in expert evidence and             the role of the expert witness  2

D    Outline of the Consultation Paper 4

CHAPTER 1                 ORIGINS AND DEVELOPMENT OF THE                            EXPERT WITNESS  7

A     Introduction  7

B     Early Origins  8

C     Special Juries  13

(1)   Introduction  13

(2)   Juries of Neighbours  14

(3)   All Female Juries  16

(4)   Juries of Foreigners  18

(5)   Juries of Merchants & Other Professionals  19

(6)   The Decline of the Special Jury  20

D    Court Assessors  23

E     Court Experts and Expert Witnesses  26

F     Theory and Nature of the Opinion Rule  28

G    A Growing Recognition of the Problems with Expert Testimony  34

H     Conclusion  38


A     Introduction  39

B     Rule against Opinion Evidence  39

(1)   Exception to Exclusionary Rule: Expert Opinion Evidence  40

(2)   Necessary Elements to Prove Necessity                   for Expert Testimony  40

C     The Categories of Expert Evidence  41

(1)   Evidence in the form of Opinion Based on            Facts Given in Court 42

(2)   Expert Evidence to Explain Complex                 Subject Matters or Technical Terminology  43

(3)   Expert evidence of fact on an issue requiring  expertise to fully comprehend, observe                    and describe  49

(4)   Expert evidence of fact, on an issue that does           not require expertise to fully observe, but is a       necessary preliminary to giving evidence in              the other four categories. 50

(5)   Admissible Hearsay of a Specialist Nature  51

D    The Scope of Expert Evidence  62

(1)   Within the Field of Expertise of the Expert 63

(2)   The Common Knowledge Rule  65

(3)   The Ultimate Issue Rule  78

(4)   Expert and Non-Expert Evidence of Fact 88

(5)   Non-Expert Opinion Evidence  91

E     The Weight and Value to be Attached to                     Expert Evidence  93

(1)   The Court Assesses the Value of the                   Expert Evidence  93

(2)   The Evidence of Lay Witnesses can be given     Greater Weight than Expert Evidence  93

(3)   Factors to be Taken into Account                          When Determining Weight 95

(4)   Conflicting Expert Testimony  96

F     Usurpation of the Role of Judge or Jury  97

G    Junk Science and the Need for a Reliability Test 101

(1)   Ireland  102

(2)   United States  105

(3)   Australia  111

(4)   England & Wales  115

(5)   A Reliability Test for Ireland?  121

(6)   Conclusion  132

CHAPTER 3                THE QUALIFIED & IMPARTIAL EXPERT:                                 DUTIES and FUNCTIONS OF                                EXPERT WITNESSES  133

A     Introduction  133

B     What is an ‘Expert Witness’?  133

(1)   Definition  133

(2)   Necessary Experience and Qualifications  138

(3)   Court Procedure for Proving Expertise  146

(4)   Relationship between an Expert Witness                      & Instructing Party  150

(5)   Conclusion  153

C     Principal Recognised Duties of Expert Witnesses  153

(1)   No Definitive List of Duties in Ireland  153

(2)   The Ikerian Reefer case  154

(3)   Summary of Main Recognised Duties  156

D    Duties of Expert Witnesses Recognised in Other Jurisdictions  173

(1)   England  173

(2)   Australia  181

(3)   Euroexpert 184

(4)   France  185

(5)   Ireland  186

E     Conclusion  194

CHAPTER 4                 Adversarial Bias, Partisanship &                  Conflicts of Interest  197

A     Introduction  197

B     Conscious Bias  197

(1)   Personal Interest 198

(2)   Financial Interest 201

(3)   Intellectual Interest 204

(4)   Bias or Genuine Disagreement 206

C     Unconscious Bias  207

(1)   Forensic Experts  207

(2)   Misunderstanding of the Role of                                the Expert Witness  211

D    Selection Bias  214

E     Conflicts of Interest 215

F     Judicial Commentary on Bias and Partisanship  217

(1)   Ireland  217

(2)   Australia  217

(3)   England & Wales  218

G    Ways to Reduce Possibility of Bias  222

(1)   Argument One: The Current Adversarial Expert Testimony System is Adequate to Combat Bias  222

(2)   Argument Two: There is a need for the         Amendment of the Adversarial Structure  224

H     Conclusion  229

CHAPTER 5                 Procedural aspects of the giving of   expert testimony  231

A     Introduction  231

B     The Need for Procedural Reforms  231

(1)   Expense  232

(2)   Delay  233

C     Selection, Appointment and Examination of Experts  234

(1)   Disclosure of Intent to Adduce Expert Evidence  234

(2)   Court Permission to Adduce Expert Evidence  235

(3)   Pre-Trial Determination of Admissibility of             Expert Evidence and of Expertise  238

(4)   Terms and Conditions of Appointment 241

(5)   Information and Instructions for Experts  243

(6)   Experts Costs and Fees  245

D    Communication between Experts and between          Experts and the Court: Pre-trial and At the Hearing  250

(1)   Pre-Trial Meetings between Experts  250

(2)   Experts Questions  255

(3)   Court Directions  256

(4)   Disclosure of all Relevant Information  257

E     Expert Reports  260

(1)   Disclosure of Expert Reports &                               Rules of Privilege  260

(2)   Exchange of Expert Reports  266

(3)   Requisite Contents of the Expert Report 267

(4)   Producing Expert Reports in Court 276

F     Alternative Structures to Party Appointed Experts  279

(1)   Single and Court Appointed Experts  279

(2)   Panels of Experts or Mixed Panels  299

(3)   Special Jury  302

(4)   Court Assessors or Advisors  304

G    Conclusion  305

CHAPTER 6                 sanctions, accountability and        governance of expert witnesses  307

A     Introduction  307

B     Training & Accreditation of Experts  308

(1)   Fraudulent ‘Expertise’ 308

(2)   Existing Examples of Training & Accreditation  309

(3)   Difficulties caused by Lack of                        Mandatory Training  317

(4)   Should Mandatory Training & Accreditation be introduced?  317

(5)   Training for Judiciary and Other Members                  of the Legal Profession  320

(6)   Training & Accreditation: Conclusion  320

C     Professional Expert Witness Regulatory &          Disciplinary Bodies  320

(1)   Dedicated Regulatory Body for                             Expert Witnesses  320

(2)   Dedicated Disciplinary Body for                           Expert Witnesses  325

(3)   Immunity from Disciplinary Action from          Professional Regulators  329

(4)   What Circumstances Should Disciplinary Action        Be Taken In?  333

(5)   Types of Professional Disciplinary Sanctions  333

(6)   Immunity Issues: Conclusion  335

D    Expert Witness Immunity from Civil or Criminal Suit 336

(1)   Ireland  337

(2)   England and Wales  344

(3)   Expert Witness Immunity from Suit: Abolition or Retention?  353

E     Alternative Remedies to Civil Suit 357

(1)   Criminal Sanctions  358

(2)   Civil Sanctions  360

F     Conclusion  362

CHAPTER 7                 SUMMARY OF provisional       recommendations  363




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(1996) EGCS 23


Abinger v Ashton

L.R. 17 Eq. 358, 373 (1873)


AG (Ruddy) v kenny

(1960) 94 ILR 185


Aird & Anor v Prime Meridian Ltd

[2006] EWHC 2338


Alsopp v Bowtrell

(1620) Cro. Jac. 541


Anglo Group Plc v Winther Brown & Co Ltd and BML (Office Computers) Ltd

[2000] EWHC Technology 127 (8th March 2000)


Armchair Passenger Transport Ltd v Helical Bar PLC

[2003] EWHC 367 QB


Ashford v Thornton

(1818) 1 B. & Ald. 405



Unreported, High Court, 23 November 2001


Barings plc v Cooper & Lybrand (No.1)

[2001] EWHC Ch 17 (9th February 2001)


Beckwith v Sydebotham

1 Camp 116


Best v Wellcome Foundation Ltd

[1993] 3 IR 421


Bird v Adams

[1972] Crim LR 174


Buckley v Rice-Thomas

(1554) Plowden 124; 75 ER 182


Bushell's Case

(1671) Vaughan 142, 22 Car. 2


Cala Homes (South) Ltd & Ors v Alfred McAlpine Homes East Ltd

[1995] EWHC 7 (ch) (06 July 1995)


Carter v Boehm

1 Smith LC, 7th ed (1876)


Clark v Ryan

(1960) 103 C.I.R. 486


Commonwealth Development Bank of Australia Pty Ltd v Cassegrain

[2002] NSWSC 980


Confetti Records v Warner Music

[2003] EWCH 1274


Daniels v Walker

[2000] EWCA Civ 508


Daubert v Merrell Dow Pharmaceuticals, Inc

509 US 579: 113 S. Ct. 2786 [1993]


Davie v Edinburgh Magistrates

(1953) SLT 54


Davis v Stena Line Ltd

[2005] EWHC420 (QB)


Derby & Co Ltd and Others v Weldon and Others

The Times, Nov 9 1990


DK v TH (Orse TK)

Unreported, High Court, February 25, 1998


Doherty v North Western Health Board, Davison and Medical Defence Union and MDU Services Ltd

[2005] IEHC 404


DPP v A and BC Chewing Gum Ltd

[1968] 1 QB 159


DPP v Boyce

[2005] IE CCA 143


DPP v Buckley

[2007] IEHC 150


DPP v Egan

[1990] ILRM 780


DPP v Kehoe

[1992] ILRM 481


DPP v Yu Jie

[2005] IECCA 95


DPP v Yusuf Ali Abdi

[2004] IE CCA 47


Dunne v National Maternity Hospital

[1989] IR 91 (SC)


English Exporters Pty. Ltd. v Eldonwall Ltd

[1973] 1 Ch 415


F v L (Orse F)

[1990] 1 IR 348


F(G) v B(J)

[2000] IEHC 112 (28th March 2000)


F(Ors C) v C

[1991] ILRM 79


Field v Leeds City Council

[1999] EWCA Civ 3013 (8 December 1999)


Fitzpatrick v DPP

Unreported, High Court 5th December 1997


Folkes v Chadd

(1782) 3 Douglas 157


Franks & Faith (t/a Ground Rent Securities) v Towse

[2000] EWLands LRA 2 1999


Frye v United States

(1923) 54 App. DC 46, 293 F. 1013


Galvin v Murray

[2000] IESC 78


General Electric Co. v Joiner

522 US 136 (1997)


Graigola Merthyr Co Ltd v Swansea Corporation

[1928] 1 Ch 31


Hanrahan v Merck, Sharpe & Dohme

[1988] IESC 1; [1988] ILRM 629 (5th July 1988)


Harmony Shipping Co v Saudi Europe

[1979] 1 WLR 1380


Hawkes v London Borough of Southwark

[1998] EWCA Civ 310 (20 February 1998)


HG v The Queen

(1999) 197 CLR 414


Hoechst Celanese Corporation v BP Chemicals Limited

[1998] EWCA Civ 1081


Huffman v Lindquist

(1951) 37 Cal 2d 465



[2005] IESC 24 (26 April 2005)



[2000] IESC 58


Joyce v Yeomans

[1981] 1 WLR 549


JWH (Orse W) v GW

Unreported, High Court, February 25, 1998


Kenning v Eve Construction

[1989] 1 WLR 1189


Kincaid v Aer Lingus Teoranta

[2003] IESC 31 (9 May 2003)


Kirin-Amgen Inc and Ors v Hoechst Marion Roussel Ltd & ORs

[2004] UKHL 46


Kumho Tyre Co v Carmichael

526 US 137 (1999)



[1992] 2 IR 11


Ladner v Higgins

71 So. 2d 242 (La. Ct. App. 1954)


Liddell v Middleton

(1996) PIQR 36


Liverpool Roman Catholic Archdiocesan Trust v Goldberg

[2001] EWHC Ch 396 (6th July 2001)


Maguire v Ardagh

[2002] 1 IR 385


McFadden v Murdock

(1867) Exchequer IR ICL 211


MCG(P) v F(A)

[2000] IEHC 11 (28th January 2000)


McGrory v ESB

[2003] IESC 45


McMullen v Farrell

[1993] 1 IR 123


Mc'Naghten's Case

(1843) 10 Cl. & Fin 200


McTear v Imperial Tobacco

[2005] ScotCS CSOH 69


Midland Bank Trust Co Ltd v Hett Stubbs & Kemp

[1978] 3 All ER 571


Mohammed v Financial Services Authority

[2005] UKFSM FSM 013 (18 January 2005)



Unreported 5th December 1997


Murphy v The Queen

[1989] 164 CLR 94


Mutch v Allen

[2001] 2 CPLR 24


National Justice Compania Naviera SA v Prudential Assurance Co Ltd (The Ikerian Reefer)

[1993] 2 Lloyd's Rep 68



SC July 5 2001


News Datacom v Lyons

[1994] IEHC 1; 1994 1 ILRM 450 (20th January 1994)


O'Callaghan v O'Sullivan

[1925] 1 IR 90


O'Doherty v Whelan

(1994) 12 ILT 25


O'Keeffe v Kilcullen

[2001] IESC 84


O'Keeffe v Kilcullen

[2001] IESC 84


O'Keeffe v Kilcullen

[2001] IESC 84


Payne v Shovlin

[2006] IESC 5 (09 February 2006)


Pearce v Ove Arup Partnership Ltd & Ors

[2001] EWHC Ch 455 (2nd November 2001


People (AG) v Fennell (No. 1)

[1940] IR 445


People (AG) v Kelly

(1962) Frewen 267


People (DPP) v Allen

[2003] 4 IR 295


People (DPP) v Fox

Unreported, Special Criminal Court, 23rd January 2002


People (DPP) v Howe

Irish Times 15 October 2003


People (DPP) v John Gilligan

Unreported 15 March 2001


People (DPP) v Pringle

(1981) 2 Frewen 57 (CCA)


Petursson & Or v Hitchison 3G UK Ltd

[2005] EWHC 920 (TCC) (09 May 2005)


Polivitte Ltd v Commercial Union Assurance Co. Plc

[1987] 1 Lloyd's Rep 379


Poynton v Poynton

(1903) 37 ILTR 54


Quarmby Electrical v Trant t/a Trant Construction

[2005] EWHC 608 TCC


R (Factortame) v Secretary of State for Transport

[2002] EWCA Civ 932


R v Abadom

[1983] 1 WLR 126


R v Abbey

[1982] 2 SCR 24


R v Barnes

[2005] EWCA Crim 1158


R v Bjordal

(1960) 103 C.I.R. 486


R v Bonython

[1984] 38 SASR


R v Cannings

[2004] EWCA Crim 1


R v Chatwood

[1980] 1 WLR 874; [1980 1 All ER 467, 70 Cr.App.Rep. 39


R v Clark (Sally)

[2003] EWCA Crim 1020


R v Dallagher

[2002] EWCA Crim 1903


R v Ferrers

(1760) 19 Howell, State Trials 924-944


R v Gilfoyle

(2001) 2 Cr. App. R. 5


R v Greene

(1679) 7 Howell, State Trials, 185, 186


R v Harris & Ors

[2005] EWCA Crim 1980


R v Heath

(1744) 18 Howell, State Trials 70


R v Howe

[1982] 1 NZLR 618


R v Johnson

(1994) 75 A Crim R 522


R v Luttrell

[2004] EWCA Crim 1344


R v Meads

[1996] Crim LR 519 CA


R v Mohan

[1994] 2 SCR 9


R v O'Brien

[2000] EWCA Crim 3


R v O'Connell

(1844) 7 Irish L. Rep 261


R v Pembroke

(1678) Ib. 1337, 1228, 1340, 1341


R v Puaca

[2005] EWCA Crim 3001


R v Robb

(1991) 93 Cr.App.R 171


R v Rouse

The Times, 24 February 1931


R v Silverlock

[1894] 2 QB 766


R v Stockwell

(1993) 97 Cr.App.R. 260


R v Toner

93 Cr App R 382


R v Turner

[1975] QB 834


R v Ugoh

[2001] EWCA Crim 1381


R v Ward

(1993) 96 Cr App R 1


Ramsay v Watson

(1961) 108 CLR 642



Unreported, High Court, December 21 2004


Re Haughey

[1971] IR 217


Re J

[1990] FCR 193


Re J

[1990] FCR 193


Re N

[1999] EWCA Civ 1452 (20 May 1999)


Richardson v Redpath, Brown & Co Ltd

[1944] A.C. 62; 36 BWCC 259


Rockwater v Technip France SA & Ors

[2004] EWCA Civ 381: [2004] RPC 46


Routestone v Minories Finance

[1997] BCC 180


RT v VP (Orse VT)

[1990] 1 IR 545


S(J) v S(C)

[1996] IEHC 23; [1997] 2 IR 506 (14th October 1996)


Severn, King and Company v Imperial Insurance Company

The Times April 14 1820


Shell & Pensions v Fell Frischmann

[1986] 2 All ER 911


Sherrard v Jacob

[1965] NI 151

N Irl

Smith v Lothian University Hospitals NHS Trust

[2007] ScotCS CSOH 08


Southern Health Board v C

[1996] 1 IR 219


Spencer Cowper

(1699) 13 Howell, State Trials, 1126-1135


Stanton v Callaghan

[1998] EWCA Cil 1176 (8 July 1998)


State (D and D) v Groarke & Ors

[1990] 1 IR 305


Strudwick & Merry

(1994) 99 Cr. App. 326


The Beryl

(1844) 9 P.D. 137


The People (DPP) v Horgan

Irish Examiner 25 June 2002


The People (DPP) v Mark Lawlor

Central Criminal Court 2 December 2005


The Torenia

[1983] 2 Lloyd's Rep 210


Thompson v Thompson

Solicitors Journal of 3rd February 1961 Volume 105


Thorn v Dickens

[1906] WN 54


Thorn v Worthing Skating Rink Co

(1877) 6 Ch D 415


Toth v Jarman

[2006] EWCA Civ 1028 (19 July 2006)


Transport Publishing Co Pty Ltd v The Literature Board of Review

(1955) 99 CLR 111


Velveski v The Queen

(2002) HCA 4 (14 February 2002)


Vernon v Bosley

[1996] EWCA Civ 1217



Unreported, Supreme Court 31 October 2003


Wallersteiner v Moir (No. 2)

[1975] QB 373


Webb v Page

(1843) 1 Car & Kir 23


Whitehouse v Jordan

[1981] 1 WLR 246


Wilband v The Queen

(1966) CanLII 3 (SCC)


Witches Case

(1665) 6 Howell, State Trials 687


Wright v Doe d Tatham

(1838) 4 Bing NC 489








A                  Background to the project

1.                 This Consultation Paper forms part of the Commission’s Third Programme of Law Reform 2008-2014,[1] and involves an examination of the current rules concerning the admissibility of expert evidence in court and the role and function of expert witnesses.  The project also involves an examination of arrangements for ensuring the quality of expert evidence.  In terms of these two key aspects of the project, the Commission also explores relevant options for reform.

B                  The admissibility of expert evidence of opinion and the role of the expert witness in court

2.                 As the detailed discussion in this Consultation Paper indicates, a key element of the law of evidence as it applies in courts is that witnesses are generally allowed to give only relevant and factual evidence; they are not permitted to express their opinion on their evidence.  For example, if a person saw a colleague having an accident while working with a machine in a workplace, he or she could give evidence in court about what happened but would not be permitted to give an opinion about whether, for example, the machine complied with national or international safety standards.

3.                 There are a number of reasons why opinion evidence by ordinary witnesses is not permitted.  One is that an opinion may be based on a “hunch” rather than actual knowledge or expertise and would therefore be unreliable.  Another reason is that the opinion – for example, as to whether a machine complies with safety standards – may be directly related to what is described as the “ultimate issue” to be decided by the court.  In any criminal prosecution of the employer under relevant safety and health legislation, the ultimate issue is whether the employer was in breach of any statutory duty to the employee and whether it has committed an offence.  Similarly, in any civil claim the ultimate issue is whether the employer was in breach of any legal duty and is required to compensate the employee for any injuries sustained.

4.                 The ultimate issue, whether of criminal or civil liability, is a matter for a court to decide, not for any witness.  The overwhelming majority of criminal trials dealt with in the Irish courts (over 200,000 annually) are heard in the District Court by a judge sitting alone, who is both the finder of fact and determiner of liability.  More serious crimes (over 2,000 annually) are in general dealt with in the Circuit Criminal Court where the court consists of a judge and jury.  Here the jury, guided by the trial judge on questions of law, is the finder of fact, while the judge determines the sentence.  Major criminal trials, in general murder and rape, are tried by judge and jury in the Central Criminal Court (over 100 annually).  In a criminal trial the ultimate issue of innocence or guilt may turn on a complex technical issue such as DNA evidence, mobile phone tracing evidence, or the interpretation of medical evidence.  In such cases, it is unlikely that a judge or members of a jury will have the detailed technical knowledge required to decide, for instance, whether a DNA profile of the accused correctly matched the DNA sample found at the scene of a crime, or whether a baby died because of violent shaking or from natural causes

5.                 The vast majority of civil trials are tried by a judge (or occasionally a number of judges) without a jury. Here, the ultimate issue to be decided may also turn on a technical issue, such as whether a particular machine complied with safety standards or whether a chemical substance complied with relevant statutory regulations. Again the court is unlikely to have the required knowledge to deal with all the varied issues that arise in civil trials.

6.                 It is clear that this is where the combination of expert evidence and the expert witness forms an important part of many criminal and civil trials. In the law of evidence, the main exception to the rule against allowing a witness to given opinion evidence is that an opinion can be given by an expert in an area of expertise outside the scope of knowledge of the court, in particular the finder of fact. The benefits of permitting the court to be assisted in its fact-finding role by expert knowledge have long been recognised. In that respect, expert evidence and expert witnesses will continue to play an important role in the courts.

C                  The challenges involved in expert evidence and the role of the expert witness

7.                 At the same time, however, the Commission is aware that expert evidence and expert witnesses present challenges. In its Report on the Establishment of a DNA Database[2] the Commission traced the recent emergence of DNA evidence in criminal trials. The Commission noted that the benefits of DNA evidence, both in exonerating the innocent and in convicting the guilty, are evident but it is also clear that this is an emerging science which presents a number of challenges. On the one hand, for example, there may be some who completely mistrust scientific evidence. On the other hand, there may be those who take the view that the expert –  perhaps especially a crime scene expert referring to DNA evidence – must always be right because they are always right when portrayed on TV.  In other instances, the problem may be with the individual expert – the testimony may be hugely relevant and convincing but it may be delivered using scientific jargon that the court (whether judge or jury) cannot follow.  In its Report on the Establishment of a DNA Database the Commission made some recommendations on how these matters might be addressed in the specific setting of DNA evidence.

8.                 The Commission is aware that the specific issues it discussed in the context of DNA evidence reflect concerns in the wider setting of expert evidence and expert witnesses generally. Increasing specialisation of knowledge in a complex society has led to an exponential growth in the number of requests to enlist the aid of experts in civil and criminal trials. This has led to an examination of this growth, with a view to ensuring that expert evidence remains available to courts while at the same time addressing concerns about its reliability.

9.                 In the Reports of Lord Woolf in the mid 1990s[3] that led to fundamental reform of civil procedure generally in the courts in England and Wales, some of the principal causes for unease with the system of giving expert evidence were outlined. In Lord Woolf’s Access to Justice, Interim Report (1995) the following comments were made:

“In many cases the expert, instead of playing the [independent and impartial] role identified by Lord Wilberforce,[4] has become… ‘a very effective weapon in the parties' arsenal of tactics.’ A similar point was made by the Commercial judges… when they summarised the present faults as follows:

·         polarisation of issues and unwillingness to concede issues from the start;

·         insufficient observance of the confines of expert evidence and expansion into the realms of rival submissions; and

·         insufficient willingness to strip out, agree or concede all but the essential issues following exchange of reports.”

10.               The Australian Law Reform Commission, which carried out a review in this area in 1999, identified some of the main challenges of expert evidence as being:[5]

11.               This Consultation Paper seeks to set out the law as it stands in Ireland on expert evidence, and examine whether the criticisms that have been raised in other jurisdictions can be applied in the Irish context. The Commission seeks to outline the problems that have been raised as well as discussing some of the potential changes that could be made to address these problems.

D                  Outline of the Consultation Paper

12.               In the light of these general introductory comments the Commission now proceeds to provide an overview of the succeeding chapters in this Consultation Paper.

13.               Chapter 1 sets out an historic overview of how expert knowledge was used in the courts along with the development of a body of evidence laws and how this has evolved into the current rule against opinion evidence, subject to the exception that allows expert opinion testimony.

14.               Chapter 2 examines the rules governing the admissibility of expert evidence. The different categories of matters on which expert evidence is admitted are outlined. This chapter also examines the precise scope and parameters of expert evidence and the rules governing this, including the requirement that the issue be outside the range of knowledge of the finder of fact and the prohibition on the giving of an expert opinion on an ultimate issue in a case. The various factors that are taken into account when determining the appropriate weight and value to attach to expert testimony in a particular case are outlined. Some of the main concerns about how expert testimony is given, the possible usurpation of the role of the jury and the possible admission of unreliable or ‘junk science’ are also identified. This chapter concludes by discussing whether there is a need to introduce some sort of reliability test, such as the Daubert and Frye tests that have been applied in the United States.

15.               Chapter 3 focuses not on the evidence but on the individuals proffered to give expert evidence. The question ‘what is an expert witness’ is addressed, along with determining the scope of the duties and function of an expert witness.

16.               Chapter 4 examines the potential problems that can arise with expert witnesses, such as a failure to act independently, in an unbiased manner or impartially, and the possibility of the experts becoming partisan ‘hired guns’ for their instructing parties. This chapter also outlines a number of ways in which bias and partisanship can be limited in the giving of expert testimony.

17.               Chapter 5 discusses some procedural changes that could be made to deal with the expense and delays involved in the current system. A range of provisions aimed at improving communication between experts, and between experts and the court, and also aimed at improving the standard of expert reports, are identified. This chapter also examines some alternative arrangements for giving expert testimony that might be introduced, in contrast to the position in Ireland at present by which the parties are responsible for the decision to adduce expert evidence and for the choice of expert.

18.               Chapter 6 examines the issue of introducing some form of accreditation, registration or training regime for experts. The range of possible sanctions that could be imposed on an expert for failing to act independently, for negligence, or for breach of duty is also discussed. In this respect, the appropriateness of having immunity from suit for expert witnesses is also debated.

19.               Chapter 7 contains a summary of the Commission’s provisional recommendations for reform as well as issues on which submissions are sought.

20.               This Consultation Paper is intended to form the basis for discussion and therefore all the recommendations made are provisional in nature. The Commission will make its final recommendations on the subject of expert evidence following further consideration of the issues and consultation with interested parties. Submissions on the provisional recommendations included in this Consultation Paper are welcome. To enable the Commission to proceed with the preparation of its Final Report, those who wish to do so are requested to make their submissions in writing by post to the Commission or by email to by 30 April 2009.





A                  Introduction

1.01             A wealth of academic literature and professional debate currently exists which focuses on the use of expert witnesses in court. This might give the impression that the use of expert witnesses is a new legal phenomenon, which has come about as a result of the increasing specialisation of knowledge in today’s society, and that it is only in recent decades that the potential criticisms and weaknesses of the expert witness system have been identified. In fact, the use of, and problems associated with, expert evidence in court has deep historic roots, and examples can be seen in case law dating from the Middle Ages.

1.02             Hand argues that an historical analysis of the rise of expert testimony is in reality no more than a gradual recognition of such testimony amid the rules of evidence as those rules began to take form. An examination of the rise of its history highlights that expert evidence has long since been accepted as necessary and beneficial, even prior to the development and enforcement of exclusive rules of evidence.[6]

1.03             The purpose of this chapter is to trace the development of the use of expert evidence from its earliest origins, and by doing so to highlight that the benefits of using such evidence, and the debate surrounding its many problems, have been evolving for several centuries.

1.04             Part B looks at the early origins of the use of experts prior to the advent of trial by jury. Part C examines and explains the concept of the special jury and gives historical examples where this structure was used.  Part D looks at the use of court assessors in this jurisdiction and in other jurisdictions over the centuries. Part E follows the rise of the use of the court expert and expert witnesses in the courts and Part F traces the growth of a formal body of evidence law to govern the use of such experts. Part G then discusses the problems that emerged due to increasing use of expert witnesses in litigation. 

1.05             This chapter concludes by summarising in Part F the current Irish position on the use of expert witnesses in court, with the aim of providing an overview of the discussion that follows in the subsequent chapters.

B                  Early Origins

1.06             The basis for allowing expert knowledge in the resolution of disputes is that such knowledge is necessary for a finding that certain facts existed. Prior to the advent of trial by jury, however, the resolution of disputes was largely founded on a judgment from God, the Judicium Dei, which involved very different principles. The older methods of proof used did not involve rational adjudications upon evidence given in support of a theory, and there was little opportunity for passing judgment on particular facts.[7]

1.07             The trial itself was, as Rosenthal describes it, “merely a submission to a mechanical process of proof.”[8] The court was simply required to decide which party should undergo the selected form of proof. Then, under the supervision of the court, this party would take an oath before God that his cause was just, and subsequently undergo some kind of test, or trial.[9] As can be seen from a brief explanation, these methods of trial did not therefore contain any provision for experts or for the development of laws of evidence, or for the use of witnesses in the modern sense.

1.08             The older methods of trial took four main forms. The best known and most commonly used method in criminal trials was trial by ordeal. This was an appeal to God to reveal the truth of human disputes and took several forms, usually requiring fire or water. For example, the ordeal of water required the accused party to be bound and lowered into a body of water; if he sank the water was said to have ‘received him’ with God’s blessing and he was quickly pulled out.[10]

1.09             Another commonly used form of ordeal involved the party with the burden of proof wrapping his hand in leaves and then holding a hot iron for a set period of time. If he emerged unscathed, his cause was considered just and he had successfully proved his case. If he burned, he lost.[11] Such ordeals were manipulable, and many undergoing an ordeal with hot iron succeeded. This may have contributed to its considerable popularity as the method of trial of choice.[12] In 1215, the Ordeal was denounced by the Church in the conciliar legislation of the Fourth Lateran Council under Pope Innocent III.[13] As the Clergy were needed to administer the oath that had backed the accusation,[14] the ordeal could not proceed without their support, and secular authorities quickly followed the Church’s example by prohibiting ordeal by fire or water as a means of resolving disputes.[15]  

1.10             Trial by battle is often considered to be a type of trial by ordeal, a “bilateral ordeal”.[16]  Here, the parties decided the issues by physical combat, the theory being that Providence would always intervene to ensure victory on the side of the right.[17] This form of trial was invoked in civil cases, and parties to the dispute would often hire champion fighters to engage in battle for them.[18] This may also explain why it was such a popular method amongst the upper classes, who would have been able to afford such unassailable competitors. This method of trial began to wane at the same time as the other early forms of proof, but was not in fact formally abolished until 1818 in the renowned case of Ashford v Thornton.[19]

1.11             Another method was the system of compurgation or wager of law where the accused took an oath that he did not commit the crime and produced eleven compurgators to back this claim and testify to his good character.[20] Initially this required eleven neighbours of the accused to testify, but with the centralisation of Royal Justice in the two benches it became costly and unnecessary to expect 11 men to be brought long distances for routine cases. As a result the system evolved to enable the defendant to hire professional compurgators to testify on his behalf and by the end of the 16th century it was the official duty of the court porters to provide them for a fee. This in effect meant the process simply amounted to the defendant’s oath coupled by a ceremony for which he paid, and the system of compurgation did not survive after 1600.[21]

1.12             Another factor in the decline of this method was the complexity involved in the oath, as the emphasis was placed here on the oath itself, rather than any probative value of the witness’ words.[22] If any of the compurgators missed even one word, the oath failed and the party lost.[23]

1.13             Related to the wager of law system was the system of proof by witnesses. This was a process whereby a party would produce a witness who would swear an oath on the veracity of that party’s version of events and attest to their good character. Essentially, success was dependant on the quantity of witnesses, and the party who could produce the most witnesses to back his claim won the lawsuit.[24]

1.14             These older forms of proof all began to decline around the 13th century amid a growing realisation that they were irrational and inconsistent methods of resolving disputes. In particular, contemporary Church reformers had become very disillusioned with such forms of proof, and appealing to the Judicium Dei to settle legal disputes was criticised as being inconsistent with the principles of theology at the time.[25]

1.15             The vacuum left by the abandonment of these methods of proof required the secular authorities to create or adopt new procedures to carry out their functions.

1.16             Trial by inquisition became the new method of choice in the majority of Western European countries. However in England, the Juries of Presentment introduced by the Assizes of Clarendon and Northampton provided the model for what later became trial by jury.[26] Through jury trial, the adjudication of disputes slowly became centred on the reasoned decision of a body of reasonable human beings who received evidence before them in the form of documents and records, rather than on the outcome of a mechanical procedure of proof. Indeed, Holdsworth argues that it is at this point that we can see an indication of the tentative beginnings of a law of evidence, for example, the introduction of provisions that witnesses should be compelled to attend and testify in common law,[27] and for the cross examination of witnesses by counsel,[28] which helped to clarify the distinction between jurors and witnesses. [29]

1.17             However, it was not the case that the law of evidence had a gradual and consistent development right from the beginning of the system of trial by jury. In fact, the earliest jury trials had few formal procedures, and an elaborate structure of rules of evidence and procedure was not initially considered necessary. The need for such a structure was only recognised towards the end of the 18th century when the English legal system underwent what has been termed the “Adversarial Revolution.” This refers to the increasing presence of lawyers in the trial process which until that point had been dominated by the judge.[30]

1.18             ‘Lawyerization’[31] led to criminal proceedings becoming more centred around the presumption of innocence, and also led to a clearer division between jurors and witnesses. As a result, rules governing probative evidence, and what matters could be presented to the jury, became extremely important. Once the trial process became organised around the notion that the elements of the case must be proven by the parties before a jury, the parties began to gain more control over production of evidence in court, and by the end of the 18th century a considerable body of evidence law had been developed.[32]

1.19             The requirement that the parties prove their case led to a realisation that the resolution of certain disputes of a technical or complex nature might well require expert or specialised knowledge. However it appears that at the outset the common law struggled to decide how best to acquire and allow such knowledge. In time, three main procedures for importing expert knowledge were developed which will now each be discussed in greater detail.  

1.20             In some instances, special juries composed of persons knowledgeable in the subject matter of the particular case were empanelled, effectively a jury of experts. Elsewhere, most notably in courts of admiralty, the court itself appointed ‘court assessors’, to advise it in matters beyond its knowledge. In these cases the court had discretion to pass instructions on to the jury or to be guided by the assessor in making its own findings.[33] Later on, expert witnesses were hired by the parties or the court, a system that has evolved into the present one. The development of these three procedures will now be discussed.

C                  Special Juries

(1)                Introduction

1.21             The first method of enhancing the knowledge of the jury was not through the use of experts as witnesses or court advisors, but in fact through ‘Special Juries.’ Oldham argues that the term ‘special jury’ can have a number of different meanings, but for the purpose of this discussion the term refers to jurors who were specially selected because their special knowledge or experience made them particularly qualified in the facts of the dispute in question, or gave them a special expertise in a particular subject matter. [34]

1.22             The concept of expert or special juries was not a new or novel development, and there are indications of this system dating from as far back as the 14th century. [35] According to Thayer;

“What we call the ‘special jury’ seems always to have been used. It was the natural result of the principle that those were to be summoned who could best tell the fact, the veritatem rei.[36]

1.23             By the end of the 19th century, the use of special juries was widespread. In England, the first legislation to provide for the regulation of special juries was An Act for the Better Regulation of Juries,[37] which provided for the use of such juries wherever they were requested by the parties or they were considered necessary. The 1730 Act was extended to apply in Ireland by sections 3 to 6 of An Act for the Amendment of the Law with Respect to Outlawries, Special Juries and the Future Effects of Bankruptcy in Certain Cases 1777,[38] and section 21 of the English Jury Act 1826.[39] The Irish Jury Act 1833[40] was the first express legislative mention of special juries in this jurisdiction.[41]

1.24             It should be noted however, a number of different types of special juries were used through the centuries; some of the most common ones will now be discussed.

(2)                Juries of Neighbours

1.25             The earliest juries were required to be entirely composed of ‘next neighbours’ i.e. members of the locality where the dispute arose.[42] The reasoning behind this was that they were likely to be knowledgeable about the events in question. They were known as ‘hundredors,’ and the jury effectively amounted to juries of neighbours.

1.26             These early jurors were permitted and in fact expected to learn the facts of the case through their own means,[43] therefore having a jury of inhabitants from the area where the event occurred increased the likelihood of their being well-informed about the event in question.[44] In time, the requirement for an entire jury made up of ‘next neighbours’ became unmanageable, and the rule was altered to require that only a certain number of the jury come from the particular ‘hundred’ in question.[45] These men were then expected to inform the other jurors of the background to the issues.[46]

1.27             However, at this time the distinction between jurors and witnesses, and how information was to be imported into the case, was unclear. The requirement that the jurors be knowledgeable about the facts of the case did not necessarily mean that their knowledge was firsthand, and it was common for jurors to consult witnesses and other sources of evidence before reaching their verdict.[47] As Holdsworth explains,

“…the issue of how a jury came by its knowledge was not originally a matter with which the law concerned itself.”[48]

1.28             The transformation from this type of jury of witnesses into a jury of impartial fact-finders took place gradually over several centuries, and a great deal of uncertainty remains regarding this transformation.[49] For a considerable period of time, the jury as witnesses coexisted with the jury as fact-finder.[50]

1.29             Gradually, however, parties were allowed to nominate witnesses to testify publicly in court, and as a result of this development of formal witness testimony, along with clearer rules of evidence and procedure, the number of hundredors required declined through a series of statutes[51] until the requirement was abolished completely for civil cases in 1705.[52] Eventually, the same result was worked out in practice for criminal cases.[53]

(3)                All Female Juries

1.30             Another early example of a special jury was the jury of matrons de ventre inspiciendo. These were all-female juries commissioned to investigate women in issues relating to disputed pregnancy and in paternity disputes. Such disputes were common in criminal cases, as a woman found guilty of a capital crime was entitled to have the death sentence delayed if she could show that she was pregnant until the child was born. In theory, on birth, the punishment of the defendant could then be carried out but in practice, due to the costs of rearing the newborn, the mother was often subsequently pardoned.[54] As Lambard put it,

“[a female defendant was entitled to] have (for once onely) the benefit of her belly, if it be found by women thereto appointed that she is with child.”[55]

1.31             In order to determine if the defendant was pregnant, the court would empanel an all-female jury under a writ de ventre inspiciendo, a writ to ‘inspect the belly.’ The jury would be sworn in[56] and would then be led to a chamber where they would search and inspect the defendant. The jury would subsequently return a verdict declaring whether or not she was ‘quick with child.’[57]

1.32             If the jury found that she was pregnant, the court would stay her punishment until the next assize. Oldham reports that there is evidence that ‘pleading her belly’ was a common phenomenon among female criminal defendants.[58] However, the defendant would only be entitled to such a reprieve once only. As Blackstone reasons:

 “But if she once hath had the benefit of this reprieve, and been delivered, and afterwards becomes pregnant again, she shall not be entitled to the benefit of a further respite for that cause. For she may now be executed before the child is quick in the womb; and shall not, by her own incontinence, evade the sentence of justice.”[59]

1.33             The writ was also occasionally used in civil cases. Blackstone explains that a jury de ventre inspiciendo would be empanelled in situations where a widow “feigns herself with child, in order to exclude the next heir, and a suppositious birth is suspect to be intended.”[60]

(4)                Juries of Foreigners

1.34             The trial of ‘aliens or foreigners’ also historically gave rise to a specially constituted jury, the jury of the half tongue, or de medietate linguae, although this type of jury was not technically designated as ‘special.’[61]

1.35             A writ de medietate linguae provided that in trials where the defendant was a foreigner, half the jury could be empanelled from juries consisting of half denizens and half foreigners, so that the trial would be more impartial.[62] Thayer argues that the reasoning behind the jury de medietate linguae, which was commonly referred to as the party jury, were considerations of policy and fair dealing, rather than on a wish to provide a well-informed or expert jury.[63]

1.36             The jury de medietate linguae in fact originated in the treatment of the Jews in medieval England. In 1190, a charter given by King Richard I allowed all Jews - who were considered resident foreigners rather than British subjects - to be tried before a half Jewish jury.[64] A century later, after the expulsion of the Jews from England, foreign merchants took over their role as the primary commercial class. As a result, at common law the right of these common merchants to be tried by a jury half composed of their own countrymen began to develop.

1.37             The right was built on in a number of statutes culminating in a statute of 1354 which codified the right to a half foreign jury where one party was a foreigner, and an entirely foreign jury where both parties were foreigners, in both civil and criminal trials.[65] Although the right was reaffirmed a century later, the party jury gradually began to decline and was banned outright in the Naturalisation Act 1870,[66] as it was no longer perceived that this was the best way to ensure that the trial was fair.

(5)                Juries of Merchants & Other Professionals

1.38             The use of special juries was also a common occurrence in trade disputes in the city of London from as early as the 1300s. Throughout the 14th and 15th Centuries, it was often the case that supervisors of the different guilds would bring cases before the mayor against those who were alleged to have committed serious breaches of the trade regulations. The mayor would subsequently summon a jury composed of men of the particular trade in question who would decide if there had been a breach of the trade regulations. The mayor would then impose sentence based on this decision.[67] Examples of breaches of trade regulations include fishing with meshes smaller than those required, improper tanning of hides, improper hats and caps, false tapestry and false wine.[68]

1.39             As well as guild supervisors bringing grievances to the mayor, it also often occurred at this time that private persons, individually or through the public prosecutor, would bring complaints that they were mistreated by a trader, for example that they were sold putrid meat or bad wine. Here also men in the same trade as the accused, and who were knowledgeable about the facts of the case, would be summonsed to give their decision, which the mayor then used in sentencing.[69]

1.40             There are many examples of cases over the centuries that followed which reveal the willingness of the court to allow juries to be specially constituted of members of certain trades or professions where it was considered necessary. Oldham cites Sayles early King’s Bench cases[70] where juries of clerks and attorneys were empanelled in cases dealing with such issues as falsification of writs by attorneys or extortion by court officials. These expert juries of enquiry became more frequent as time went on as the problem of corrupt behaviour of court officers persisted.[71]

1.41             In 18th century London, largely under the auspices of Lord Mansfield, the aid of merchant juries was more and more frequently invoked. This had a significant contribution on the development of a body of commercial law.[72] Legislation was enacted to provide for the use of special juries wherever they were requested by the parties or were considered necessary.[73] Such juries were very commonly used in insurance cases, or cases involving bankers’ customs, as it was considered that the special jurors’ experience provided a helpful source of knowledge and expertise for the court and the parties to the case.[74]

1.42             However, such juries were not only commonly used at this time within the commercial field; they were also widely used in business disputes such as bankruptcy and debt, as well as a broad range of criminal and civil actions such as libel, slander, conspiracy, criminal conversation, bribery, trespass, assault, assumpsit, trover, replevin, debt, mandamus, actions for ejectment, actions upon bills of exchange, and bonds.[75]

(6)                The Decline of the Special Jury

1.43             By the mid 19th century, special juries were being requested by parties not to provide specialist knowledge, but to ensure a higher class of juror than would otherwise appear, and special juries were available wherever a party was willing to pay for it.[76] As Sir William Erle commented while testifying before the Select Committee on Special and Common Juries of the House of Commons which was set up to examine the function of juries:

 “I believe the intention of the Legislature has been departed from, and to my mind a very pernicious custom has been introduced, whereby the right to resort to a special jury has been so given as to foster the notion of there being class prejudices pervading the jury box, and that a party wanting to rely on a certain class of prejudice, would take one jury, or the other accordingly.”[77]

1.44             Further allegations of corruption and abuse of the special jury system emerged around this time, for example a scathing review by Jeremy Bentham on Jury Packing. In this, he referred to special juries as “an engine of corruption,” and “the Guinea Trade,” and called special jurors “Guineamen,” a reference to the fact that a successful profession could be made as a juryman as they were paid one guinea per case (in sharp contrast with the shilling or eightpence paid to common jurors).[78]

1.45             A more caustic description given to special jurymen was “Guinea pigs,” which highlights the underlying feeling that the authorities were capable of manipulating the selection process to ensure that only chosen men formed the panel of jurors. [79]

1.46             Another problem that was increasingly recognised at the end of the 19th century is the fact that the special jury system was being abused where a defendant sought to delay the trial or gain more time. The defendant would obtain a rule for a special jury, and this effectively resulted in the trial being postponed.[80]

1.47             Two major statutory reforms were enacted to address these criticisms. The County Juries Act 1825,[81] sought to enhance the qualifications and quality of special jurors by requiring them to be merchants, bankers, esquires, or persons of higher degree, however, the absence of an express definition of these terms led to inconsistent and discretionary application of the Act’s provisions in different localities. [82] The act also set up a system of anonymous balloting for the selection of jurymen in order to address criticisms about jury packing.[83]

1.48             The Juries Act 1870[84] further attempted to redeem the special jury system by establishing further procedural rules for special jurors,[85] and by altering the qualification requirements of special jurors.[86] However, despite these attempted reforms, the special jury’s popularity continued to decline, and in the Juries Act 1949 it was abolished in England in all but the very narrowest category of cases.[87]

1.49             The abandonment of the special jury occurred earlier in this jurisdiction, as section 66 of the Juries Act 1927 provided for the abolition of the two-tiered system of jurors.[88]

D                  Court Assessors

1.50             An alternative to enlisting the aid of a special jury that has been used over the centuries by common law courts, most commonly in admiralty cases, was the use of court assessors, or advisors. The purpose of this was to give the court specialist experience, skill or knowledge which it might not normally possess.[89] A concise definition is provided by Dickey who describes a court assessor as:

“[A] person who, by virtue of some special skill, knowledge or experience he possesses, sits with a judge during judicial proceedings in order to answer any questions which might be put to him by the judge on the subject in which he is an assessor.”[90]

1.51             The use of assessors originated in the admiralty courts, and the earliest reported example dates from the 16th century.[91] Although there are examples of other courts enlisting the aid of assessors, they were most frequently invoked in nautical proceedings.  Statutory provisions remain in force which allow for the appointment of court assessors in court proceedings generally[92] but their actual use, outside nautical proceedings, appears to be limited to patents cases and railway investigations.

1.52             There were many similarities between a court assessor and an expert witness, as the function of both is to furnish the court with specialist knowledge and information in areas in which they are particularly skilled. Indeed, in some cases assessors were referred to as witnesses, and the information they provide as evidence, a practice that was criticised by Viscount Simons L.C. in Richardson v Redpath, Brown & Co Ltd.[93]

“To treat…any assessor, as though he were an unsworn witness in a special confidence of the judge, whose testimony cannot be challenged by cross-examination and perhaps cannot even be fully appreciated by the parties until judgment is given, is to misunderstand what the true functions of assessors are. He is an expert available for the judge to consult if the judge requires assistance in understanding the effect and meaning of technical evidence.”

1.53             This demonstrates that the problem with referring to assessors as witnesses is that key differences existed in reality in the way the two carried out their role and duties.  Expert witnesses were appointed and remunerated by the parties whereas assessors were appointed by the court and remuneration depended on the governing statute or the discretion of the court. Furthermore, assessors were not witnesses and so were not sworn and were not subject to cross examination.

1.54             Another difference lies in the fact that assessors are required to furnish the court with advice, in private, to enable it to make its decision, not to bolster the arguments of a party. Therefore, they are not concerned with the weight or balance of evidence, and should not be asked to decide on the issues.[94] The distinction between the two is supported by the rule, recognised in a number of English cases throughout the 18th century, that expert evidence cannot be adduced on a matter within the scope of knowledge and experience of assessors assisting the court.[95]

1.55             Although it appears that there is considerable value attached to the role of assessors, unease was expressed in a number of cases in the 19th century with their function.[96] Regardless of the advice given, it is still the function of the judge to decide on the issues, but increasing concern began to be raised that judges might not fully appreciate this fact and might attach undue importance to the assessors’ views. In The Beryl[97] case Brett L.J. stated, in the context of nautical proceedings:

“The assessors who assist the judge take no part in the judgment whatsoever: they are not responsible for it, and have nothing to do with it. They are there for the purpose of assisting the judge by answering any question, as to the facts which arise, of nautical skill.”

However, later on he recognised the reality that:

“Still, it would be impertinent in a judge not to consider as almost binding upon him the opinion of the nautical gentlemen who, having ten times his own skill, are called to assist him.”[98]

1.56             The perceived danger that a process whereby a judge receives undisclosed specialised knowledge or advice from an assessor whose is under no obligation to disclose the advice given to the judge could lead to an effective transfer of the decision making function from judge to assessor, might well account for the general decline in the use of court assessors. Today, they are most frequently appointed in nautical proceedings and their use elsewhere is limited.

E                  Court Experts and Expert Witnesses

1.57             The use of special juries declined in the early 20th century and the use of expert witnesses, who were summoned to give advice to the court, greatly increased. However, expert witnesses first made tentative appearances much earlier than this.

1.58             There are many examples of cases dating from as far back as the 14th century where skilled persons were summoned to assist the court and, as is evident, when later on concrete rules of evidence were being developed and enforced, the use of expert witnesses continued despite the rule prohibiting opinion evidence.

1.59             Initially, the court itself would summon skilled persons to assist it in deciding on a question of fact where it did not possess the requisite knowledge. As early as 1345, in an appeal of mayhem,[99] the court enlisted the aid of experts when surgeons from London were summoned.[100] Here, the question to be decided by the court was if the appellant should be entitled to bring a case before them, a question which hinged on whether or not his wound was fresh, and thus whether it amounted to a mayhem.[101]

1.60             Similarly in 1494 ‘masters of grammar,’ were summoned to explain the meaning of a Latin word to help construe a bond[102] and in 1554 the court in Buckley v Rice-Thomas[103] confirmed that in the context of the case at hand it should be permissible for the court to call grammarians where its own Latin was lacking.[104] Saunders J used the opportunity to give a general statement on when the use of experts might be accepted:

“If matters arise in our law which concern other sciences or faculties, we commonly apply for the aid of that science or faculty which it concerns. Which is an honourable and commendable thing in our law. For thereby it appears that we do not despise all other sciences but our own, but we approve of them and encourage them as things worthy of commendation.”[105]

1.61             To further this argument, Saunders J cites earlier examples of cases where the court enlisted the aid of experts in coming to its decision. Amongst these:

“….a case where excommengement was pleaded against one, and the party said he ought not to be disabled thereby, because there was an appeal pending thereof, there the Judges enquired of them that were well versed in the canon law touching the force thereof”[106]

1.62             This demonstrates that the practice at this time was for the court, rather than the parties to call the experts. Holdsworth explains that experts at this time were more in the kin of “expert assistants to the court” than witnesses called by the parties, which “naturally prevented any question from being raised as to their information in the aspect of testimony to the jury.”[107]

1.63             Therefore while the court enlisted the aid of experts, they were not expert witnesses in the modern sense, because as Rosenthal argues, “We can look for the expert witnesses only when proof of facts by witnesses, rather than by the personal knowledge of the tribunal, becomes accepted.”[108]

1.64             In 1562 the Statute of Elizabeth was passed which compelled witnesses to appear in court.[109] This greatly contributed to the development of the modern system of deciding the case on the basis of the testimony by witnesses before the jury and by the mid 17th century, a clearer distinction could be made between jurors and witnesses. By the 18th century the adversarial system and the concept of proof by witnesses before the jury had firmly taken shape.

F                  Theory and Nature of the Opinion Rule

1.65             As mentioned above, by the end of the 18th century, once the notion that parties were responsible for their own proof in court had taken hold, they began to gain more control over production of evidence and examination of witnesses in court, and a considerable body of evidence law had been developed.[110] A number of exclusionary rules developed to govern the content and presentation of evidence before the jury, most notably the rule against hearsay, which sought to limit witness testimony to that based on personal observation, and the opinion rule, which sought to control the way in which witnesses gave their testimony.[111]

1.66             The opinion rule remains one of the chief exclusionary rules of evidence today and provides that witness testimony in the form of opinion or inference is inadmissible in both civil and criminal proceedings, and witnesses are confined to giving evidence of facts. The doctrine was in fact summarised as early as 1651 by Vaughan C.J. in Bushell's Case;[112]

“The verdict of a Jury and Evidence of a Witness are very different things, in the truth and falsehood of them; a Witness swears but to what he hath heard or seen, generally or more largely, to what hath fallen under his senses. But a Juryman swears as to what he can inferr and conclude from the Testimony of such Witnesses by the act and force of the Understanding, to be the Fact inquired after, which differs nothing in the Reason, though much in the punishment, from what a Judge, out of various cases consider’d by him, inferrs to be the Law in the Question before him.”

1.67             Wigmore argues that in the 18th century when the rule began to develop, it was concerned with testimonial qualifications and so sought to ensure that only ‘men of science’ would testify on ‘matters of science.’[113] However, nowadays the primary rationale for the rule is that it prevents witnesses from usurping the role of the tribunal of fact whose job it is to make inferences and reach conclusions on the basis of facts placed before them. As per Kingsmill Moore J in the more recent case of AG (Ruddy) v Kenny:[114]

“It is a long standing rule of our law of evidence that, with certain exceptions, a witness may not express an opinion as to a fact in issue...It is for the tribunal of fact – judge or jury as the case may be – to draw inferences of fact, form opinions and come to conclusions.”[115]

1.68             Wigmore contends that a related purpose of the rule is to ensure that unnecessary testimony is not placed before the jury, as he explained:

“[w]herever inferences and conclusions can be drawn by the jury as well as the witness, the witness is superfluous.”[116]

1.69             The opinion of an ordinary witness is thus seen as having no useful bearing on the case. This rationale was also referred to by Kingsmill Moore J in AG (Ruddy) v Kenny,[117] where he explained that the rule ensures that possible hazards such as “prejudice, faulty reasoning and inadequate knowledge,” which might be introduced if a witness were allowed to give opinion evidence, are avoided.[118]

1.70             The development in the exclusionary rule of opinion evidence in the 18th century was accompanied by the simultaneous development of a wide exception to the rule in favour of expert witnesses. It can be seen that the ‘expert witness’ developed as an exception to the developing adversarial structure, as according to Golan, it was “the only type of witness the new system could not rationalise under its evolving doctrines.” [119]

1.71             Expert witnesses became a distinct legal entity from other witnesses, as they were not required to observe the facts of the case personally in order to be permitted to give an opinion on them in court.[120] In the absence of any other legal test, the opinion rule therefore provides the principal legal distinction between ordinary and expert witnesses.[121]

1.72             This exception to the opinion rule in favour of experts is well evidenced by examples from the late 17th century onwards where experts were permitted to give testimony of their conclusions to the jury. For example in Alsopp v Bowtrell[122] the jury accepted the testimony of physicians who argued in a disputed legitimacy case that a child born forty weeks and nine days after the death of the mother’s husband could well be his child, as the birth could have been delayed by ill usage and lack of strength.

1.73             In the Witches Case[123] a doctor summoned to testify clearly believed the accused persons were witches and supported this belief with a scientific explanation of the fits they underwent. However, it is not clear from the judgment who called the doctor to testify.[124]

1.74             In the 1678 murder trial R v Pembroke[125] physicians were called by both sides to testify as to the real cause of the deceased’s death and as to whether or not a man can die of his wounds without fever. Hand points out that the only striking feature of this case is that at no stage in the course of proceedings was the giving of such testimony seen as unusual.[126] This implies that the giving of opinion evidence by experts was by this stage an accepted exception to the rule against opinions.

1.75             Similarly, in a case from the following year, R v Greene,[127] a physician was summoned by the prosecution to support the theory that the victim’s death could not have been caused by wounds on his body as there was no blood and that he must have therefore died of strangulation.

1.76             There are several cases dating from the 18th century which show that by then the practice of giving expert testimony was well settled and accepted.[128] However, the rules of evidence also began to be more strictly enforced, including the general rule excluding the opinion of witnesses who were not experts.

1.77             This was emphasised in R v Heath[129] a perjury case where the defendant swore that Lady Altham had never had a child. In the course of proceedings, a witness, who had testified he had seen Lady Altham with “a big belly” was asked “what do you apprehend became of that big belly?” The court stressed that the opinion of a witness can only be given where it is the best evidence available in the case, highlighting the exclusionary nature of opinion evidence.[130]

1.78             Similar developments took place in civil cases. Folkes v Chadd,[131] is regarded as the seminal precedent that established the admissibility of expert testimony and confirmed that expert witnesses could testify directly to the jury as a witness for either party.[132] Here, a trespass action was taken against the defendant for threatening to cut down an embankment erected by the plaintiffs to prevent overflowing of the sea on to the plaintiff’s land. The defendants argued that they were justified and entitled to cut down the embankment as it had caused the flooding of the harbour leading to extensive damage.

1.79             On appeal, Lord Mansfield ordered a new trial on the basis that the testimony of a renowned engineer in favour of the plaintiffs, which amounted to an opinion about the cause of the damage, should have been held admissible. It had been argued that the testimony should be excluded as it “was matter of opinion, which could be no foundation for the verdict of the jury, which was to be built entirely on facts, and not on opinions.”[133] This however was rejected by Lord Mansfield who used this opportunity to outline the parameters of the admissibility of expert testimony:

“It is objected that Mr. Smeaton is going to speak, not as to facts, but as to opinion. That opinion, however, is deduced from facts which are not disputed – the situation of banks, the course of tides and of winds and the shifting of the sands….The question then depends on the evidence of those who understand such matters; and when such questions come before me, I always send for some of the brethren of the Trinity House.[134] I cannot believe that where the question is, whether a defect arises from a natural or artificial cause, the opinions of men of science are not to be received….the cause of the decay of the harbour is also a matter of science, and still more so, whether the removal of the bank can be beneficial. Therefore we are of the opinion that his judgment, formed on the facts, was very proper evidence.”[135]

1.80             The development of the opinion rule gave rise to another related rule of evidence namely the requirement for a hypothetical question where the expert has not observed the facts at issue himself. This limits the questions that can be asked of the expert where he does not have personal observation, and provides a means for the jury to test the opinion by explaining the grounds for the opinion.[136]

1.81             The hypothetical question requirement is first to be seen in cases from the late 17th and early 18th century when the distinction between ‘opinion’ and ‘fact’ became more clear. Hand cites the celebrated murder case of Spencer Cowper[137] where the question arose whether the deceased had been drowned and where surgeons and sailors were enlisted to answer hypothetical questions on the circumstances under which a deceased body would sink.

1.82             In the murder trial R v Ferrers[138] the accused raised the defence of insanity. To support this defence, a number of lay witnesses were called to testify about the purported insane acts committed by the defendant. Subsequently, a surgeon was called and asked if he would conclude based on the facts and the testimony of the preceding witnesses, that the defendant was insane. Pursuant to the Crown Counsel’s objection to this line of questioning, Lord Mansfield held that the defendant was not entitled to put such a general question to the surgeon but that he could specify the specific facts, already submitted in evidence, on which the surgeon would base his opinion, even though the surgeon had not had firsthand experience of the purported acts of the defendant.[139]

1.83             Similarly, in Beckwith v Sydebotham,[140] Lord Ellenborough confirmed that expert witnesses were entitled to be summoned, even where they had not had firsthand experience with the facts of the issue. However, the point was stressed that they were required to give their opinion on the basis of hypothetical questions:

“As the truth of the facts stated to them was not certainly known, their opinion might not go for much; but still it was admissible evidence. The prejudice alluded to might be removed by asking them, in cross-examination, what they should think upon the statement of facts contended for the other side.”[141]

1.84             Much discussion on the issue was given in Mc'Naghten's Case[142] in 1843 where the question arose if a medical expert could rule on the sanity of the accused at the time of the crime from the testimony of the witnesses at the trial, without having firsthand experience of the accused prior to the trial. The majority of the Justices held that he could not be asked his opinion on such issues, as explained by Tindal J:

“...because each of those questions involves a determination of the truth of the facts deposed to, which it is for the jury to decide, and the questions are not mere questions upon a matter of science, in which case such evidence is admissible.”[143]

1.85             Tindal J’s judgment highlights that the requirement for hypothetical questions has largely been motivated by a need to prevent the usurpation by the expert of the jury’s power and function to decide on the facts of the case. However Wigmore argues that, beneficial as the hypothetical question rule is,

“Misused by the clumsy and abused by the clever, [it] has in practice led to intolerable obstruction of truth.”[144]

G                  A Growing Recognition of the Problems with Expert Testimony

1.86             The foregoing discussion demonstrates that the adversarial system also had a significant effect on the manner in which experts gave their opinions in court. Whereas previously experts were drafted in by and to be of assistance to the court, from the 18th century onwards, as demonstrated by Folkes v Chadd,[145] experts began to be directly employed by the parties themselves to help advance their respective cases. Golan explains that “as the court assumed a neutral position, free reign was increasingly given in the courtroom to partisan views.”[146]

1.87             However, decisions from this time show a considerable lack of unease about the potential problems that could arise with the switch from court appointed, independent and impartial expert advisors to partisan ‘experts for hire.’ For example in Folkes v Chadd,[147] Lord Mansfield explained his decision to allow the opinion of the expert engineer on the basis that “the opinion of men of science” can be of considerable value where the issue in question is “a matter of science.”[148] As such, he failed to refer to the fact that the particular man of science in question had been specifically selected by one of the parties to advance their case.

1.88             Golan argues that this shows little awareness of the potential difficulties that might arise with partisan experts.[149] He points out that the failure to identify potential problems proved unfortunate, as “by the mid 19th century partisan expert testimony become an acrimonious and persistent thorn in the side of the common law.”[150]

1.89             As the 19th century progressed, the growth and spread of industry meant the types and quantity of expert witnesses appearing in trials had rapidly increased. At the same time, an undercurrent of dissatisfaction with the expert witness system had become stronger and its opponents louder.

1.90             In Severn, King and Company v Imperial Insurance Company[151] the types of problems that could arise with expert testimony, such as conflicting experts, became apparent. Here, the plaintiff’s sugar factory had been destroyed by fire and they took a civil case against the defendant insurance company to recover their losses when the company refused to pay out compensation. The defendants argued that they were entitled to refuse to pay out as their contract with the plaintiffs had been rendered void by the fact that the plaintiffs had, without informing the insurance company, introduced a new method of sugar purification three months prior to the fire, and that this method was considerably more dangerous than the previous method used.

1.91             At trial, the case essentially consisted of conflicting evidence from a torrent of distinguished men of science on either side testifying as to the dangers involved in the different methods of sugar refining, arguments backed up with contradictory definitions, observations and experiments and conflicting evidence.[152] According to Dallas CJ:

“[the experts] left the court in a state of utter uncertainty; and the two days during which the results of their experiments had been brought into comparison, were days not of triumph, but of humiliation to science.”[153]

1.92             The Times reported Dallas CJ’s harsh criticism of the partisanship and bias evident from the conflicting experimental evidence adduced by experts on both sides:

“It must be a matter of general regret to find the respectable witnesses to whom [Dallas CJ] was alluding drawn up, not on one side, and for the maintenance of the same truths, but, as it were, in martial and hostile array against each other.”[154]

1.93             Similar criticisms were made about the practice of ‘shopping’ for partisan or biased experts by Jessell LJ in Thorn v Worthing Skating Rink Co:[155]

 “A man may go, and does sometimes, to a half-a-dozen experts. I have known it in cases of valuation within my own experience at the Bar. He takes their honest opinions, he finds three in favour and three against him; he says to the three in his favour, will you be kind enough to give evidence? And he pays the three against him their fees and leaves them alone: the other side does the same. It may not be three out of six, it may be three out of fifty. I was told in one case, where a person wanted a certain thing done, that they went to sixty-eight people before they found one.”[156]

1.94             As these cases demonstrate, by the mid 19th century, judges were increasingly critical of ‘expert shopping’ and of those expert witnesses who acted as partisan advocates for the party they represented manifested by the experience of experts being in constant conflict. Experts employed in such cases were highly paid, therefore, as Golan puts it:

 “…their conduct was seen as the corruption of their science, of selling its credibility to the higher bidder.”[157]

1.95             Despite these criticisms, and despite numerous calls from both members of the scientific and legal communities for reform of the system of expert testimony to the effect that the expert witness would be employed independently from the parties or as an advisor to the court itself, as the 19th century progressed the system remained one whereby clients could shop around to find an expert who would give a suitable opinion. As Golan explains;

“The scandals were frequent, but they were generally justified by the legal profession as a price worth paying in what was believed to be a competitive free market of legal evidence that constituted both the best mechanism of proof-testing and the best protection from abuse of executive power.”[158]

1.96             At the end of the 19th century therefore, the expert witness, in the modern sense of the term, had become a key figure in court proceedings. As we shall see in the following chapters, over time stricter admissibility and procedural requirements have been applied to the system of expert testimony which has helped to reduce the potential for abuse.

1.97             However, the historic analysis in this chapter reveals that the key criticisms of expert testimony, still frequently raised today, have existed ever since expert witnesses have been used in the courts and therefore this debate is not a new but a considerably antiquated one.

H                  Conclusion

1.98             Today, the opinion rule, which holds that witness testimony in the form of opinion is inadmissible in both civil and criminal proceedings, and that witnesses are confined to giving evidence of facts, is firmly entrenched in the rules of evidence. As per Kingsmill Moore J in AG (Ruddy) v Kenny:[159]

“It is a long standing rule of our law of evidence that, with certain exceptions, a witness may not express an opinion as to a fact in issue...It is for the tribunal of fact – judge or jury as the case may be – to draw inferences of fact, form opinions and come to conclusions.”[160]

1.99             The admissibility of expert evidence is the principal exception to the rule. An opinion may be given by a witness who has expertise in a particular area that is relevant to the issue at hand. The purpose of this exception is that such evidence provides the judge or jury with the necessary specialist criteria for testing the accuracy of their conclusions, and enables them to form their own independent judgment by applying these criteria to the facts proven in evidence.[161]

1.100          In order to adduce expert evidence, the party will need to prove that the evidence is needed in the circumstances and that the person in question is suitable to give expert evidence on the issue. The burden of proof of expertise rests on the party wishing to adduce the witness in evidence.

1.101          It is ultimately the decision of the court to allow evidence of experts. The two main requirements that a party must satisfy in order to be permitted to adduce expert evidence in court are;

·           It must be shown that the expert evidence is necessary and relevant in the circumstances

·           It must be established that the witness is a qualified expert

1.102          These two requirements will be discussed in greater detail in the following chapters.






A                  Introduction

2.01             This chapter sets out the current rules and procedures relating to the use of expert evidence in Ireland. Part B outlines the main rules of evidence which apply to the giving of expert testimony and the necessary elements that need to be proved. Part C lists the various categories of issues which the court allows to form the subject matter of expert testimony.

2.02             Part D examines the permitted scope of expert testimony and discusses how the court determines how a particular matter is outside the range of knowledge of the finder of fact. Part E discusses the reasons behind the development of strict rules of evidence applying to expert witnesses by highlighting some of the problems that can arise in this regard, including the possibility of the usurpation by the expert witness of the role of the judge or jury.

2.03             Finally, Part F queries whether there is a need to impose an additional barrier to admissibility to ensure expert evidence is reliable by introducing a formal reliability test that all parties seeking to adduce expert evidence would have to satisfy.

B                  Rule against Opinion Evidence

2.04             The general rule is that witness testimony in the form of opinion is inadmissible in both civil and criminal proceedings, and witnesses are confined to giving evidence of facts. The primary rationale for this rule is that it prevents witnesses from usurping the role of the tribunal of fact whose job it is to make inferences and reach conclusions on the basis of facts placed before them.[162] As Kingsmill Moore J stated in AG (Ruddy) v Kenny:[163]

“It is a long standing rule of our law of evidence that, with certain exceptions, a witness may not express an opinion as to a fact in issue...It is for the tribunal of fact – judge or jury as the case may be – to draw inferences of fact, form opinions and come to conclusions.”[164]

(1)                Exception to Exclusionary Rule: Expert Opinion Evidence

2.05             The main exception to the exclusionary rule is that an opinion may be given by a witness who has expertise in a particular area which is relevant to the issue at hand. The purpose of this is to provide the judge or jury with the necessary specialist criteria for testing the accuracy of their conclusions, and enable them to form their own independent judgment by applying these criteria to the facts proved in evidence.[165]

2.06             This was considered by Kingsmill Moore J in AG (Ruddy) v Kenny[166] where he explained that:

“…the nature of the issue may be such that even if the tribunal of fact had been able to make the observations in person he or they would not have been possessed of the experience or the specialised knowledge necessary to observe the significant facts, or to evaluate the matters observed and to draw the necessary inferences of fact.”[167]

2.07             Based on the inherent subjectivity and potential for difficulties with opinion evidence the exception to the exclusionary rule is strictly interpreted. As will be discussed below, the admissibility of expert evidence is governed by a number of rules and conditions in terms of the types of issues on which expert opinion evidence will be permitted and the scope of evidence that can be given.

(2)                Necessary Elements to Prove Necessity for Expert Testimony

2.08             In order to be authorised, the party will need to prove that expert evidence is needed in the circumstances and that the person in question is suitably qualified to give expert evidence on the issue. The burden of proof of expertise rests on the party wishing to adduce the witness in evidence.

2.09             The two main requirements that a party must satisfy in order to be permitted to adduce expert evidence in court are;

i)                   It must be shown that the expert evidence is necessary in the circumstances in that it is relevant and that it has probative value.

ii)                   It must be established that the witness is a qualified expert.

2.10             The first of these requirements will now be examined in greater detail by considering the various categories of expert evidence that have been recognised and, once the evidence is considered as falling within a permitted category, the scope of any such evidence that may be given.

2.11             The second of these categories involves an examination of how the courts have interpreted the concept of an expert for the purposes of the giving of expert testimony. This will be looked at in greater detail in chapter three.

C                  The Categories of Expert Evidence

2.12             As a general rule, expert evidence will be allowed in relation to all matters that are outside the scope of the knowledge and expertise of the finder of fact. As Pigot C.B. pointed out in McFadden v Murdock,[168] expert evidence can be given;

 “…wherever peculiar skill and judgment, applied to a particular subject, are required to explain results, and trace them to their causes.”[169]

2.13             Notwithstanding this generality, Hodgkinson and James have identified a number of different categories of evidence that can be given by expert witnesses.[170] They find that five such categories of expert evidence can be distinguished.

i)                   Expert evidence of opinion, based on facts that have been adduced before the court.

ii)                  Expert evidence to explain technical or complex subject areas or the meaning of technical terminology.

iii)                 Expert evidence of fact, on an issue that requires expertise to fully comprehend, observe and describe.

iv)                Expert evidence of fact, on an issue that does not require expertise in order to fully observe, comprehend and describe, but which is a necessary preliminary to the giving of evidence in the other four categories.

v)                 Admissible hearsay of a specialist nature.

2.14             These categories however undoubtedly overlap and evidence sought to be given in a particular case may easily fit into a number of different categories.

(1)                Evidence in the form of Opinion Based on Facts Given in Court

2.15             Expert opinion evidence is admissible in respect of any matter requiring expertise that is necessary to explain a result or fact that is admitted in court. It has long been recognised by the common law that “the opinion of scientific men upon proven facts may be given by men of science within their own science.”[171]

2.16             Ultimately whether the court will admit expert evidence will depend on the particular issues which a party seeks to prove, and whether or not proof of these issues would be assisted by expert evidence. However, if the issue is one on which the finder of fact is qualified and capable of forming a sound opinion, no expert evidence will be permitted as additional expertise will essentially be superfluous. The principles governing the scope of expert evidence and assessing the boundaries of knowledge of a jury or court will be discussed below.

(a)                Types of Expert Opinion Evidence

2.17             Expertise has however since expanded far beyond the traditional boundaries of professional expertise as the growth in demand for specialised knowledge has led to related growth in the demand for specialist expertise in increasingly complex issues.

2.18             Another recent phenomenon is the development of a dedicated ‘litigation support industry.’ This describes the trend where certain persons have developed skills which are solely geared towards providing expert evidence, for example accident reconstruction and care experts.[172]

2.19             The significantly lucrative nature of the expert evidence ‘industry’ has fuelled this exponential growth, but also highlights the risk that the process could be abused for profit if left unregulated. However, the list of categories of subjects is not exhaustive and continues to expand.

2.20             Persons regularly called as experts are those in the medical field such as physiotherapists, occupational therapists and psychologists who are often called in personal injuries cases or to give an opinion on the mental state of an individual.

2.21             Other growing areas of expertise include forensic accounting and computer analysis to tackle the rise in fraud cases, engineering, actuary, insurance, handwriting comparison and recognition, accident investigation, facial mapping and identification, DNA, blood, urine, blood-alcohol and drug-testing, educational issues, art-related matters such as antiques, and ballistics.[173]

2.22             Where experts have been appointed to give opinion evidence about particularly technical or scientific concepts, they may be required to give a great deal of factual background about the complex concepts on which they base their opinion. Therefore, this category of evidence often overlaps with the categories discussed below, and in reality the evidence given by most experts will entail a mixture of expert opinion and specialised fact.

(2)                Expert Evidence to Explain Complex Subject Matters or Technical Terminology

2.23             One of the more common reasons a party seeks to have expert evidence adduced, effectively the ‘bread and butter of expert evidence,[174] is to explain complex, technical, or scientific topics to a judge or jury that is completely unacquainted with these concepts.

(a)                Types of Factual Expert Evidence

2.24             Whilst expert evidence of fact can be adduced on any issue that requires it, in practice there are a number of technical and scientific areas that typically form the subject matter of factual expert evidence.

(i)                 DNA Principles and Terminology

2.25             In recent years, the use of DNA evidence in trials, particularly in criminal trials by the prosecution, has burgeoned. However, although the public at large is now tentatively acquainted with the principles underlying the use of such evidence, most of this knowledge has been imparted through the media, television and film, and thus the public perception of such evidence may be inaccurate. As a result, expert evidence continues to be necessary in any case involving DNA evidence to explain to the jury the complex principles of DNA technology and evidence.[175]

(ii)               Patent Cases

2.26             Expert witnesses are also frequently called in patent cases, as the concepts involved are particularly intricate. Malek notes that experts are called in patent cases to explain the technical terms employed, to instruct the court on the relevant principles involved, to explain the nature, working, characteristic features and probable mechanical results of an invention, as well to identify old and novel concepts in the specification, outline the extent of scientific advancement, and also, to point out differences and similarities with rival inventions and explain the significance of these similarities and differences.[176]

2.27             An interesting development in England occurred in a patent infringement case involving DNA, Kirin-Amgen Inc and Ors v Hoechst Marion Roussel Ltd & Ors[177] where the House of Lords was, with the consent of the parties, given a series of seminars in camera prior to the case by a Professor of Biochemistry at Oxford University to explain the relevant aspects of recombinant DNA technology. As pointed out by Lord Hope:

“This had the result of shortening the length of time that it was necessary to devote to the hearing by several days…it is a course which might usefully be adopted in the future in cases of this kind, where the technology is complex and undisputed and the parties are willing to consent to it.”[178]

(iii)              Foreign Law

2.28             Expert evidence will be required in order to explain and prove foreign law. In O'Callaghan v O'Sullivan[179] Kennedy C.J. held that where an issue of foreign law arises it must be “proved as a fact…it must be so proved by the testimony and competence of expert witnesses shown to possess the skill and knowledge….required for stating, expounding, and interpreting that law.”[180]

2.29             However, expert evidence is not permitted to prove a matter of domestic law, presumably as this will not be considered an issue that should be outside the knowledge of the finder of fact.[181]

(iv)              Customs and Practices of a Trade or Profession

2.30             Expert evidence will also often be given by individuals well versed and well qualified to give a detailed account of the normal practices and procedures of a particular skill, trade or profession.

2.31             For example, it has been held in several Irish decisions that evidence can been admitted to demonstrate the general practice of conveyancing solicitors in performing searches on properties,[182] to explain what the correct rent would be for a property of a certain size in a certain area,[183] to outline the general practice of medical practitioners in medical negligence cases,[184] and to explain trade customs in particular professions, such as the giving of holiday pay[185] or the losses that would be incurred under certain sales conditions.[186]

2.32             The admissibility of expert evidence concerning customs and practices was considered in McMullen v Farrell[187] where Barron J held that evidence could be admitted about the nature of a solicitor’s duty to his client and the everyday practice of solicitors. He relied on the decision of Oliver J in Midland Bank Trust Co Ltd v Hett Stubbs & Kemp[188] who held:

“Clearly, if there is some practice in a particular profession, some accepted standard of conduct which is laid down by a professional institute or sanctioned by common usage, evidence of that can and ought to be received.”[189]

(v)           Technical or Scientific Terminology

2.33             Non-opinion expert evidence may be required to interpret the correct meaning to be applied to a technical term in a document such as a will or contract, or to prove that a seemingly ordinary word had a particular meaning in the context in which it was used, where such meaning is in dispute between the parties. For example in Thorn v Dickens[190] expert evidence was admitted to show that the testator had intended to gift his property to his wife by using the term ‘all to mother’ as it was the custom in the testator’s locality to refer to one’s wife as mother.[191]

2.34             In another patent infringement case, Hoechst Celanese Corporation v BP Chemicals Ltd,[192] Aldous LJ held that in deciding the meaning of technical words, a judge is entitled to hear expert evidence from “the notional skilled man in the art”, as there is no presumption in existence which finds that where words are used that can have a technical meaning, they were intended to be given their technical meaning:

“…it would be wrong to start the task of construction with any preconceived idea. Having obtained the knowledge of the notional skilled man, the [patent] Specification must be read as a whole to ascertain its meaning and from that the court has to decide the ambit of the monopoly claimed using the guidance in the Protocol [to the European Patent Convention].”[193]

2.35             Furthermore, in construction, intellectual property, or patent disputes, the terms at issue are often outside the range of knowledge of the trier of fact, and so the aid of experts is needed to explain complex concepts where the parties are in dispute about the meaning of the term.[194]

2.36             However, the courts are flexible regarding the meaning of the ‘skilled man’, and in the interpretation of technical or complex concepts or language, copious qualifications or academic experience will not always be necessary, depending on the concept that needs to be interpreted.

2.37             For example in the copyright infringement case Confetti Records v Warner Music[195]one of the claimant’s arguments was alleged derogatory treatment of a rap song that he had composed, due to the overlay of the song with a rap containing references to violence and drugs.[196] In order to determine this issue, the court had to interpret the lyrics of the rap, many of which were in slang commonly used by drug dealers. As pointed out by Lewison J;

 “This led to the faintly surreal experience of three gentlemen in horsehair wigs examining the meaning of such phrases as “mish mish man” and “shizzle (or sizzle) my nizzle”.”

2.38             Ultimately the claimant’s argument of derogatory treatment failed as Lewison J held that although that the words of the rap were in a form of English, they were for practical purposes a foreign language, and thus required an expert in such language to interpret, which the claimant had failed to prove.

2.39             Lewison J appeared to be of the opinion that the requisite expert on such matters would be a drug dealer acquainted with such terminology, although he admitted that “the occasions on which an expert drug dealer might be called to give evidence in the Chancery Division are likely to be rare.”

(vi)          Meaning of Foreign Words

2.40             The court may also receive expert evidence as to the meaning of foreign words, where the language is out of the range of knowledge of the court, but the legal effect of these words remains a matter for the courts to determine.[197]

2.41             The service provided by translators can also be considered under this category of expert evidence.[198] The right to an interpreter is laid out in Articles 5 and 6 of the European Convention on Human Rights[199] as incorporated into Irish law by the European Convention on Human Rights Act 2003. Court translators are commonplace nowadays in many cases coming before the Irish courts, and the Courts Service have access to interpreters in 210 languages and dialects through the use of private agencies.[200]

2.42             However, the use of such interpreters in Ireland has been the subject of much criticism, as it has been pointed out that no process is provided where interpreters can be trained and tested and no qualifications are necessary or required in order to work as a court interpreter.[201]

2.43             In the Court of Criminal Appeal decision in The People (DPP) v Yu Jie[202] one of the applicant’s grounds for appeal was based on the fact that the interpreter provided by the Gardaí to question to applicant while in custody, was in fact a Chinese policeman who was working for Interpol. This fact was not made known to the applicant at the time, but he discovered this by looking at the interpreter’s laptop during the course of questioning.

2.44             The applicant argued that the realisation that it was a Chinese police officer may have in some way inhibited the Applicant, particularly as there is no right to silence under questioning in his own country.

2.45             The Court of Criminal Appeal rejected that any impropriety had taken place in respect of the interpreter, finding no suggestion that the interpreter was biased or acted from any improper motive or was in any way intimidatory towards the applicant.

2.46             However, this case does raise the possibility that interpreter services and their lack of regulation within the court system could become an increasingly common ground for appeal or challenge in cases in the near future.

2.47             The Commission provisionally recommends that further research be conducted into the functioning of translators in our court system in order to ascertain if reforms need to be taken to improve access to justice.

(3)                Expert evidence of fact on an issue requiring expertise to fully comprehend, observe and describe

2.48             This will overlap to a certain extent with the previous category, particularly where scientific evidence such as DNA technology is at issue. Expert evidence will be needed both to explain the principles of such science or technology and to describe and explain in a factual manner the results or outcomes of tests or experiments, and also often to carry out these tests and experiments, submitted as evidence. However, the court is not under any obligation to accept experiments and tests that have been conducted by experts as evidence.[203]

2.49             In the English case R v Meads,[204] the evidence against the defendant was an admission which police officers claimed to have recorded in contemporaneous handwritten notes during various interviews. The defendant argued that the admissions were fabrications and sought to introduce an experiment as expert evidence in the form of a timed re-enactment of the alleged interviews.

2.50             The prosecution had argued that the new evidence was inadmissible on the basis that it constituted opinion evidence founded on an insufficiently organised body of knowledge. However, this was rejected by the English Court of Apperal, which held that the evidence was expert evidence of fact, as no specialist skill or knowledge was needed to relay it, and was no more opinion evidence than that of a police officer who times a journey in order to test the veracity of an alibi.

2.51             However, as can be seen in R v Harris & Ors[205] even where expert witnesses are interpreting the results of factual evidence such as scientific tests, they still may disagree as to the meaning of the results, which highlights that this type of evidence will often still be in the form of opinion rather than fact.[206]

2.52             Furthermore, even if the experts are in agreement about the results of the tests, they may still be in dispute about the significance of these results for the case at hand. In this case, the English Court of Appeal accepted that:

 “…even on the interpretation of objective evidence there can be two views expressed by highly experienced and distinguished medical experts.”[207]

(4)           Expert evidence of fact, on an issue that does not require expertise to fully observe, but is a necessary preliminary to giving evidence in the other four categories.

2.53             Hodgkinson and James note that this category does not strictly come within the definition of expert evidence but argue that it is worthy of discussion due to the fact that it often forms an inseparable part of the evidence given by an expert.[208]

2.54             The type of evidence envisaged by this category was described by Hobhouse J in The Torenia[209] as being factual evidence that is used to support or contradict the opinion evidence. Such evidence is common, as in giving their expert opinion experts necessarily rely on their expertise and their experience and refer to that experience in their evidence.

2.55             Examples of this is where an expert will refer to other cases and how they apply to the case at hand, or where an expert gives evidence about past experiments or experiments conducted for the purposes of the case at hand.[210] This category will inevitably overlap with the following category of admissible hearsay.

(5)           Admissible Hearsay of a Specialist Nature

2.56             The hearsay rule operates to exclude as evidence any out-of-court statements that are offered for the purpose of proving the truth of their contents.

2.57             In the context of expert evidence, the hearsay rule applies to provide that in order to be admitted, the primary sources and facts upon which the expert’s evidence is based must be proved by admissible evidence given by either the expert himself or by other witnesses.[211]

(a)           Exceptions to the Hearsay Rule

2.58             Nowadays, there are many recognised exceptions to the hearsay rule, both statutory and at common law, which may operate to admit the evidence given by a particular expert if the evidence in question is of a specialist nature and comes within one of the recognised exceptions.

(i)            Ireland

2.59             In fact, in civil proceedings the number of exceptions that have been identified is so wide-ranging that the rule has been practically abolished, and its abolition was recommended by the Commission in its Report on The Rule Against Hearsay in Civil Cases.[212] However, it will still often apply in criminal proceedings and much uncertainty remains as to the extent of its application in the criminal context.

2.60             Materials used by experts in giving their opinion may be permitted under one of the existing common law or statutory exceptions to the rule against hearsay for example if the material is a published work, record or document of a public nature, is a statement contained in a business record, or is considered part of the res gestae.[213]

(ii)           England

2.61             In England, the operation of the hearsay rule is now largely governed by statute, with recent civil and criminal legislative reforms that have greatly helped to clarify the admissibility of this evidence.[214]

2.62             In civil proceedings, the rule against hearsay was abolished by Section 1(1) of the Civil Evidence Act 1995.[215] Hearsay in criminal proceedings is covered by Part 11 of the Criminal Justice Act 2003. Section 114 of the 2003 Act put eight common law exceptions to the hearsay rule on a statutory basis. In the context of expert witnesses, section 118 allows evidence to be admitted if it falls under:

“Any rule of law under which in criminal proceedings an expert witness may draw on the body of expertise relevant to his field.”

2.63             Section 127 of the 2003 Act further provides that preparatory statements prepared for the purposes of criminal proceedings by an expert or a member of the expert’s team can be adduced in evidence by the expert to form part of his or her expert opinion.

2.64             No comparable legislation exists in this jurisdiction but, as will be discussed below, the Irish courts have held on a number of occasions that the materials used by an expert are admissible in evidence as a permitted exception to the hearsay rule.

(b)           The Requirement for Proof: The ‘Factual Basis’ Rule

2.65             As already mentioned, if the primary facts forming the basis of the expert’s opinion are not proved in admissible evidence little weight will be attached to the opinion.[216]

2.66             This ‘basis’ rule has long since been recognised. In Wright v Doe d Tatham[217] the point was made that:

“The cautious rules by which the rejection of evidence is determined, affect as well the most weighty opinions, as the most worthless gossip, unless vouched by the indispensable sanction of an oath; a certain and few well known cases only excepted.”[218]

2.67             Similarly, in the Australian case Ramsay v Watson,[219] Dixon J stressed that:

“Hearsay evidence does not become admissible to prove facts because the person who proposes to give it is a physician.” [220]

2.68             The proof requirement takes into account the reality that it is not the expert that decides on the facts in issue, and it is ultimately the finder of fact who decides whether to accept or reject the expert’s opinion. In order to properly determine the value of the expert’s opinion, the court must necessarily be knowledgeable about the facts on which this opinion is based.

(c)           Avoiding the Proof Requirement – The Hypothetical Question

2.69             A way of avoiding this requirement to some extent could be the use of the hypothetical question, where the expert stresses that his opinion is based on a proviso that certain facts or events were true or will be proved, if not his opinion should be discarded.[221]

2.70             If an expert is giving opinion evidence in the form of a hypothesis, he or she is required to firmly explain that the conclusion reached by the expert has no factual basis but assumes the existence of a number of factors which have not been proven in evidence.

(d)           Exceptions to the Proof Requirement

2.71             Greater flexibility however is given in relation to inferences or opinions drawn from primary facts that have been proven in court. The practical reality of specialisation that an expert acquires from study or experience is that such expertise or knowledge base will usually be founded, partly at least, on material of which the expert does not have firsthand experience.

2.72             For example, as early as the 19th century in this jurisdiction, in McFadden v Murdock[222] Pigot CB rejected the argument that an expert trader should not be entitled to give an account of the losses incurred in the course of his own trading experiences because such facts cannot be proved. Pigot CB held in the alternative that such evidence, once similar to the facts which form the subject matter of the controversy, should be admissible “in illustration” of the opinion of the expert.[223]

2.73             Thus, an exception to the proof requirement grew out of necessity as well as out of recognition of the greater ability of the expert than the court to evaluate the reliability of background hearsay, as it was recognised that, as when dealing with complex subject matters, juries proved less able to draw the necessary inferences from the facts deposed.[224]

(i)            Expert’s Ability to Rely on Materials from their Field of Expertise

2.74             Nowadays, in reaching a conclusion, the expert is permitted to rely on prior studies, statistics and research, academic literature and works of reference in their field of expertise. This has been termed ‘non-specific hearsay.’[225]

(I)            England

2.75             In R v Abadom,[226] Kerr L.J. referred to this practical reality and expressed the view that:

“it is no more than a statement of the obvious that, in reaching their conclusion, [experts] must be entitled to draw on material produced by others in the field in which their expertise lie…once the primary facts on which their opinion is based have been proved by admissible evidence, they are entitled to draw on the work of others as part of the process of arriving at their conclusions.”[227]

(II)                Canada

2.76             In Wilband v The Queen[228] Fauteux J. explained the reasoning behind this by pointing out that such evidence does not affect the rule against hearsay as the material in question is not being submitted to prove its veracity but rather to explain the thought processes and knowledge bases which helped the expert to form his opinion:

“…the value of [an expert’s] opinion may be affected to the extent to which it may rest on second-hand source material; but that goes to the weight and not to the receivability in evidence of the opinion, which opinion is no evidence of the truth of the information but evidence of the opinion formed on the basis of that information.”[229]

(III)          Ireland

2.77             The issue was also considered in this jurisdiction in The People (DPP) v Boyce.[230] One of the grounds of appeal was the contention that expert evidence was admitted to include an unproven factor. The appellant argued that since the expert witness had relied on statistical information in scientific literature and could not give evidence of his own knowledge he should not have been allowed to given expert evidence on the basis of such statistics or databases. The Court summarised the principles governing this area:

“Any primary fact relied upon by the expert must be proved by admissible evidence but there are other secondary matters such as established scientific norms, practices, standards and reference points within the field of expertise….which he or she may rely upon or the like.”

The Court continued;

“In a long established exception to the hearsay rule, an expert can ground or fortify his or her opinion by referring to works of authority, learned articles, recognised reference norms and other similar material as comprising part of the general body of knowledge falling within the field of expertise of the expert in question.”

(ii)               Expert’s Ability to Rely on General Experiences from Field of Expertise

2.78             It has also been held that, in coming to an expert opinion, an expert is entitled to assess the facts against previous experiences that he or she may have had dealing with similar issues, as long as the comparable evidence does not amount to hearsay evidence of facts.

2.79             Megarry J. in English Exporters Pty. Ltd. v Eldonwall Ltd[231] attempted to explain the distinction between the requirement that the expert have personal knowledge of the facts upon which his opinion is based, and the fact that he is entitled to rely on these facts in forming his opinion and in this way is not subject to the rule against hearsay in the same way as a witness of fact;

“Basically, the expert’s factual evidence on matters of fact is in the same position as the factual evidence of any other witness. Further, factual evidence that he cannot give himself is sometimes adduced in some other way, as by the testimony of some other witness who was himself concerned in the transaction in question, or by proving some document which carried the transaction through, or recorded it; and to the transaction thus established, like the transactions which the expert himself has proved, the expert may apply his experience and opinions, as tending to support or qualify his views. That being so, it seems to me quite another matter when it is asserted that a valuer may give factual evidence of transactions of which he has no direct knowledge, whether per se or whether in the guise of giving reasons for his opinion as to value. It is one thing to say “From my general experience of recent transactions comparable with this one, I think the proper rent should be £x": it is another to say "Because I have been told by someone else that the premises next door have an area of x square feet and were recently let on such-and-such terms for £y a year, I say the rent of these premises should be £z a year….It therefore seems to me that details of comparable transactions upon which a valuer intends to rely in his evidence must, if they are to be put before the court, be confined to those details which have been, or will be, proved by admissible evidence, given either by the valuer himself or in some other way. I know of no special rule giving expert valuation witnesses the right to give hearsay evidence of facts…I can see no compelling reasons of policy why they should be able to do so.”[232]

(iii)              Expert’s Ability to Rely on Second Hand Information in Order to Form an Expert Opinion

2.80             Where the expert does not have firsthand knowledge of the facts upon which his opinion is based, for example a psychiatrist or psychologist who bases his evaluation of a patient on statements or events narrated to him by the patient, it may be nevertheless permissible for him to state a hypothesis on these assumed facts.[233]

2.81             In cases involving delay in sexual abuse cases, psychiatrists are often recruited to testify about the reasons for the delay. In such cases, it has been held that the psychiatrists are entitled to believe the complainant at face value and use the information in their opinion.

2.82             Such statements are admitted as evidence for the reason that these psychiatrists and psychologists have qualified as experts in diagnosing the behavioural symptoms of individuals, and have formed an opinion on the basis of these statements, which the trial judge deems to be relevant to the case.

2.83             However, it is important to note that these statements are not admissible as proof of their truth but rather as indicating the basis upon which the medical opinion was formed in accordance with recognised professional procedures.[234]

2.84             Thus an expert opinion based on second-hand evidence is admissible, if relevant. Furthermore, it is apparent that a distinction can be drawn between the requirement for first hand evidence, which if not present, will reduce the weight to be given to the opinion of the expert, and the rule against hearsay. The hearsay rule does not operate to exclude an expert opinion based on second-hand evidence because this evidence is not admitted to prove the fact of what the expert has been told.[235]

2.85             In the Canadian case R v Abbey[236] the accused’s psychiatrist and not the accused himself, testified, in the course of his opinion, to events related to him during several interviews. There was no admissible evidence brought before the court in respect of any of these events. On appeal Dickson J held that a retrial should be ordered as the testimony of the expert;

“…while admissible in the context of the opinion, was not in any way evidence of the factual basis of these events and experiences. The trial judge in his decision fell into the error of accepting as evidence of these facts, testimony which if taken to be evidence of their existence would violate the hear-say rule.”[237]

(e)                Hearsay and Expert Evidence: Irish Examples

2.86             A series of nullity cases in this jurisdiction considered the above principles in detail. In F v L (Orse F)[238] Barron J. held that hearsay evidence by the petitioner and two other witnesses would be disregarded and, insofar as the consultant psychiatrist related matters told to him by others in the absence of the respondent, then the Court could not accept them as true but only as statements made to him in the course of his profession in relation to a matter authorised by the Respondent.

2.87             Similarly, in RT v VP (Orse VT),[239] the respondent objected to expert opinion evidence given by an expert for the petitioner, a psychiatrist, concerning the mental state of the respondent, as hearsay, as the witness had never met or examined the respondent. The expert had based this opinion on statements from the petitioner and on a report written by the court appointed expert, also a psychiatrist, who had examined the respondent.

2.88             Lardner J upheld this objection stating that an expert witness is entitled to give an opinion on facts which are admitted or proven by himself or other witnesses, or matters of common knowledge, or upon a hypothesis based thereon, but evidence based on an individual he had never met or examined was inadmissible as hearsay.

2.89             McGrath submits that it seems incorrect to classify such evidence as hearsay, considering that in this case both the petitioner and the court-appointed expert were called to give evidence in court. He argues that it would have been more appropriate to object to the evidence on the grounds of its lack of probative value, and so this is a matter which should go to the weight rather than admissibility of the evidence. [240]

2.90             However a more lenient approach was taken by O’Higgins J in two later nullity cases, JWH (Orse W) v GW[241] and DK v TH (Orse TK).[242] In both cases, which were decided on the same day, evidence was admitted from psychiatrists concerning the mental state of the respondents even though the respondents had not been examined by the experts. O’Higgins J warned that such evidence would be of limited value due to the lack of input from the respondent but felt that this should be taken into account in assessing the weight and not the admissibility of the evidence.

2.91             An even more relaxed view to the admissibility of expert evidence was taken in State (D and D) v Groarke & Ors.[243] Here the petitioners contested the validity of a ‘fit person’ order, [244] which provided for the removal of a child from its parents, on grounds that fair procedures had not been followed in the making of the order. In particular, the petitioners objected to the evidence adduced by the respondents; a video of a doctor interviewing the child with the aid of anatomical dolls, which had formed to a large extent the opinion of this doctor that the child had been abused.

2.92             The Supreme Court allowed this evidence to be admitted, finding that the court should have before it the basic evidence (in this case the video recording and an explanation from the expert witness doctor regarding the meaning of the use by the child of the dolls) that was used to form the basis of the doctor’s opinion that the order should be made, in order to determine if this conclusion was correct.[245]

2.93             In Southern Health Board v C[246] similar facts were involved. Here, a father objected to videotape evidence of an interview between his child and a social worker, which formed the basis of an allegation of sexual abuse, being admitted in court in proceedings to impose a fit person order on grounds that such evidence amounted to hearsay. The Supreme Court held that the evidence was rightly admitted.

2.94             O’Flaherty J took the view that the videotape evidence was not hearsay evidence as it did not constitute independent evidence of the child but a material part of the expert testimony of the social worker.

“[W]e point out that the key evidence as far as this part of the case is concerned will be that offered by the social worker, Mr. Jim O’Leary. In a sense, the tapes are simply material that will back up his testimony. Essentially however, the important evidence will be his expert testimony.”[247]

2.95             The Court also found that it was a matter for the District Court to accept or reject this expert testimony, and that it remained open to the respondent to employ their own expert witness to cross examine the social worker in order to assist him in meeting the allegations.

2.96             McGrath argues that these decisions push back traditional boundaries regarding the type of evidence that is admissible in support of expert testimony and highlight the potential for the rules regarding expert evidence to be used as a backdoor means of admitting hearsay evidence.[248]

2.97             However it is important to note that in both cases much emphasis appeared to be placed on the welfare and best interests of the child. The cases did not involve a determination of the veracity of the allegations or of a prosecution of the alleged perpetrators. It is questionable if such an approach would have been taken if criminal proceedings were being taken, or the truth of the allegations was to be determined.

2.98             A more recent case dealing with potential hearsay in the evidence of the expert witness is MCG(P) v F(A).[249] Here, the parties sought court direction about the scope and extent of the powers of the expert witness in the case, a medical inspector who was appointed by the court under Order 70 Rule 32, Rules of the Superior Court for the purposes of the petition of a degree of nullity.

2.99             More specifically, the parties wished to determine if the medical inspector, an experienced consultant psychiatrist, was entitled to interview third party informants, in respect of his diagnosis of the state of mind of the parties around the time of the ceremony of marriage. The medical inspector pointed out that his expert assessment would be less complete and satisfactory from his point of view as a medical expert unless he interviews third-party informants as would often be usual in making a clinical diagnosis where personality disorder is suggested.

2.100          Budd J accepted that it would be desirable to have as much information as possible available to the medical inspector, however, he pointed out that the wording of the provisions of the statute and of the rules governing the appointment of a medical inspector envisages an inspection of the parties themselves and not an examination of third-party informants and felt that it:

 “…would stretch the elasticity beyond breaking point to extend matters to include interviewing third-party informants and this would be in breach not only of the letter but also of the spirit of the wording of the statute and of the rules.”[250]

2.101          Budd J also stressed the point that the ultimate responsibility of deciding whether or not to grant a decree of nullity was not that of the medical inspector, but of the court. He held that in order to ensure that the court remains in control of the inquiry, and for the other reasons cited, third party informants should not be interviewed.

2.102          He also seemed largely motivated by the danger that the evidence given by third party informants may be later exposed to be false. As he reasoned:

“The report based on the psychiatrist’s expertise and interviews only with the parties avoids the problem of the Court having to work out how much of the inspector’s report is based on what the inspector heard from a witness whose evidence the Court has not heard or whose evidence the Court has rejected as false…There are very real problems in reality about a Court having to extrapolate sound parts of an Inspector’s report which have not been tainted by hearsay or evidence which has been rejected. A further consideration is that the Court is seen to be in control of the proceedings and that justice is seen to be done and the perils from hearsay and loss of confidence on the part of the parties in the conduct of the proceedings from an expanded role of the medical inspector…If the inspector has based part of his assessment on contaminated evidence then this is going to cause problems in the future when his report is considered by the Court and there may be real difficulties in unscrambling the part of the omelette which has been contaminated by hearsay or false and rejected evidence.” [251]

2.103          This case shows a return to the strict view that if objection to evidence from an expert witness is raised on grounds of hearsay, such evidence is likely to be ruled inadmissible, and highlights that the court remains, as per Budd J:

 “….chary of widening the scope of the inquiry and of intermeddling by persons who may be partisan and who are not actually called to give evidence by one of the parties before the court.”[252]

2.104          McGuinness J considered the role of evidence of delay in cases of child sexual abuse in VW v DPP:[253]

“All such evidence is open to challenge in cross-examination. It must however be borne in mind that it is not the task of the expert witness to assess the credibility of the complainant or the guilt or innocence of the applicant. The truth or otherwise of the complaints is to be tested at the trial.”

D                  The Scope of Expert Evidence

2.105          There are a number of rules governing the exact parameters of the evidence that may be given by an expert. The general rule relating to opinion evidence is an exclusionary one – a witness is not entitled to give an opinion or draw inferences from facts observed; they can only testify as to the facts observed by them personally.

2.106          Expert evidence operates as a limited exception to this strict exclusionary rule. The court’s reluctance to admit opinion evidence stems from its inherent subjective nature and its ability to lead to inconsistencies and injustices. As Lord Pearce stated:

“Human evidence shares the frailties of those who give it. It is subject to many cross-currents such as partiality, prejudice, self-interest and, above all, imagination and inaccuracy.”[254]

2.107          As a result, the operation of the exception in favour of expert opinion evidence and the scope of such evidence that will be considered admissible are circumscribed by a number of ancillary rules which are strictly applied.

(1)                Within the Field of Expertise of the Expert

2.108          It is a well accepted common law requirement that the expert must confine himself to expressing an opinion on issues that are within the ambit of his area of expertise,[255] and an expert witness cannot express an opinion on legal or technical issues raised in the case, or the merits of the plaintiff’s and defendant’s arguments.

2.109          As distinguished above, in some cases an expert will only be required to outline the scientific or technical facts as understood by him. In other cases the expert will be asked to give an opinion on a set of circumstances based on his expertise. The problem arises where the distinction between fact and opinion breaks down and the expert ends up expressing a more detailed opinion than is permissible.

(a)                Defining the Parameters of Expertise

2.110          Experts are entitled to give non-opinion expert evidence, such as describing the concepts involved in a patents case or explaining the principles of DNA technology, however, the courts are strict to ensure that in doing so the experts do not go further and comment for example, as to whether the defendant’s invention infringed the plaintiff’s patent.

2.111          This is because such matters are for the judge or jury to decide as the expert witness is not, by reason of his expertise, any better placed to give an opinion on such matters than the judge or jury as such matters do not amount to specialised knowledge.

2.112          There is a danger that if an expert was entitled to give an opinion based on the expert facts outlined, excessive weight will be given to this by members of the jury and also that it may effectively amount to the expert trying the issues of the case.

(b)               England

2.113          One case where the English courts had to decide on the parameters of the expertise of the expert was R v Barnes.[256] Here, the Court of Appeal refused the appellant the right to introduce fresh evidence from an arboriculturalist, or wood grain expert, to the effect that the wood grain pattern on a fingerprint allegedly taken from a wooden door at the scene of a crime and matching that of the defendant, did not match the wood grain of the door itself.

2.114          The Court held that while the witness was undoubtedly an expert on wood grain, he had no expertise in the interpretation of lifts, or in the identification of wood-grain on lifts, which were the questions in issue, therefore his evidence was not considered of sufficient relevance to form the basis of an appeal.

(c)                Ireland

2.115          In an Irish case, The People (DPP) v Yusuf Ali Abdi,[257] the defendant appealed his conviction for the murder of his baby son on the grounds that the Court had erred in law by permitting an expert witness psychologist to give opinion evidence about the applicant’s motive in killing his son. He argued that such an opinion did not come within the ambit of a psychologist’s expertise.

2.116          He based this argument on the decision in The People (DPP) v Egan[258] and argued that the purpose of a psychiatrist is solely to offer an expert opinion as to whether the accused was insane or not at the time of the killing, and questions of intent and motive are matters for the jury, as they are matters of ordinary human experience.

2.117          The evidence in dispute was that of a consultative psychiatrist, who had prepared a report on the applicant which was used in evidence during the trial. In this report the psychiatrist had stated a belief that the defendant’s alleged actions were motivated by “his inability to accept that he would be unable to rear his child in his own religious faith coupled by the threat of losing custody of the child.”[259]

2.118          The Court of Criminal Appeal held, however, that the material was rightly admitted. The Court noted that, in two previous cases relied on, insanity had been neither established or alleged, as both were cases where it was sought to establish that the accused could avail of the defence of provocation in that he was suddenly and totally deprived of his self control, which was plainly a matter for the jury to consider and beyond the proper reach of expert testimony. The case at hand, the Court held, differed greatly. In the present case insanity was specifically alleged and pleaded, and the defence had called expert evidence to establish it. The prosecution was plainly entitled therefore to counter this with expert testimony of its own.

2.119          There are several other examples from this and other jurisdictions where expert testimony has been objected to on the grounds that the expert was giving evidence on an issue that did not come within the ambit of his area of expertise. This shows a readiness on behalf of the courts to ensure that the confines of expert evidence are firmly observed.

2.120          The majority of the objectionable evidence in these cases is however excluded as a result of the ‘common knowledge’ or ‘ultimate issue’ rules, and these two rules operating together have the effect of strictly excluding all evidence that is likely to result in the role of the finder of fact from being usurped.

(2)                The Common Knowledge Rule

2.121          Even if the matter in question falls within one of the categories of expert evidence identified above and thus comes within the range of matters for which expert testimony is permitted, if the jury is capable of making inferences from the factual testimony presented, that is, where the issue in question is within the scope of knowledge and competency of the tribunal of fact, any extra expert evidence will be superfluous and so is inadmissible. As Lawton LJ stated in R v Turner[260]

 “An expert's opinion is admissible to furnish the Court with scientific information which is likely to be outside the experience and knowledge of a judge or jury. If on the proven facts a judge or jury can form their own conclusions without help, then the opinion of the expert is unnecessary.”[261]

2.122          Evidence relating to matters of common knowledge, matters which can be dealt with by the trier of fact by applying common sense and life experience is therefore inadmissible.

2.123          The primary rationale for the exclusionary rule is to prevent the function of the judge or jury from being usurped by allowing an expert to decide on matters which are within the province of the finder of fact. Another underlying concern of the rule is to prevent excessive time wasting in trials by limiting the type of expert evidence that comes before the court.

(a)                Operation of the Rule in Common Law Jurisdictions

2.124          The rule excluding matters of common knowledge from the scope of expert testimony has been reaffirmed on several occasions in this jurisdiction and in England for centuries. However, recent cases indicate an easing of the rule, and there are many examples of inconsistent case law on this issue.

2.125          Much judicial commentary exists which strongly confirms that expert witnesses will not be permitted to give evidence on matters which are considered within the scope of knowledge of the finder of fact.

2.126          In the Australian case Transport Publishing Co Pty Ltd v Literature Board of Review[262] Dixon C.J. stated that “ordinary human nature, that of people at large, is not the subject of proof by evidence, whether supposedly expert or not.”[263]

(i)                 England

2.127          In R v Turner,[264] the accused had bludgeoned his girlfriend to death after she confessed her infidelity to him. The court refused evidence the of a psychiatrist that such an event was likely to have caused an explosion of rage in him, as “jurors do not need psychiatrists to tell them how ordinary folk who are not suffering from any mental illnesses are likely to react to the stresses and strains of life.”[265]

2.128          The reasoning behind this view is a recognition of the fact that when an expert makes a determination on an issue on which a judge or jury would be well capable of forming their own opinions and drawing their own conclusions on, the judge or jury is prone to attach greater significance than is perhaps warranted to the opinion of the expert. In R v Turner[266] Lawton LJ made reference to this:

“If, on the proven facts, a judge or jury can form their own conclusions without help, then the opinion of an expert is unnecessary. In such a case, if it is dressed up in scientific jargon it may make the judgment more difficult. The fact that an expert witness has impressive scientific qualifications does not by that fact alone make his opinion any more helpful than that of the jurors themselves; but there is a danger that they may think it does.”

2.129          Sopinka J’s comments in the Canadian case R v Mohan[267] are also in this vein:

 “…dressed up in scientific language which the jury does not easily understand and submitted through a witness of impressive antecedents, this evidence is apt to be accepted by the jury as being virtually infallible and as having more weight than it deserves.”

(ii)               Ireland

2.130          The ‘common knowledge’ rule has also been enforced by the Irish courts on several occasions. Turner was approved in Ireland in The People (DPP) v Kehoe,[268] a case with similar facts, where the Court of Criminal Appeal held a psychiatrist’s evidence about the accused’s state of mind should not have been admitted as it merely sought to articulate more fully the defence of provocation of the accused, which the accused was in a position to give to the jury himself.

2.131          Similarly, in McMullen v Farrell[269] although Barron J. admitted expert evidence about the everyday professional practice of solicitors, he refused to admit evidence relating to the manner in which litigation is conducted as he felt the court itself has factual knowledge of this practice.[270]

(b)           Difficulties Determining Matters of Common Knowledge – A Move Away from the Common Knowledge Rule?

2.132          The distinction between facts that require expertise and facts that are within the range of knowledge of the finder of fact is not always clear and difficulties can arise in certain areas. This is apparent from the case law where it can be seen that the rule against matters of common knowledge has occasionally received disparate and inconsistent application.

2.133          Deciding on admissibility and policing the boundaries of what is within the knowledge of the finder of fact is made more difficult by the fact that these boundaries can change with developments in science and technology.

2.134          One area where considerable difficulties have arisen is whether or not expert testimony should be admitted on the credibility of the accused.[271] This is particularly so in criminal trials, probably due to the presence of the jury and the view that they might afford greater weight to expert evidence than is appropriate or than would a judge.

2.135          However, there are some limited examples of cases where expert evidence on the credibility of the accused has been admitted; where it is considered that the issue of credibility is outside the experience and knowledge of the jury; as this is a more reliable indicator than attempting to define whether or not the evidence relates to a recognised mental illness or not.[272]

(i)            Ireland

2.136          The emergence of new and specialised areas of expertise has led to difficulties in determining whether an issue is something which a lay judge and jury are capable of assessing, or whether expert evidence on the issue is necessary.

2.137          In The People (DPP) v Pringle[273] the accused argued that expert forensic evidence, which amounted to a comparison of fibres found on cars used in a bank raid and those found on the accused’s pullover, should not have been admitted as the judges were competent to make such a comparison themselves.

2.138          The court however rejected this, placing considerable emphasis on the expertise of the witness in forensic science, and expressed the view that requiring judges to personally conduct “laboratory experiments….for visual comparisons” as being “novel and wholly inappropriate.”[274]

2.139          Psychiatric and psychological expert evidence has generated considerable difficulties. In Kehoe, O’Flaherty J was of the opinion that medical expert evidence such as that of psychiatrists should properly be confined to matters such as insanity and other forms of mental illness. In borderline cases the court may decide to allow expert evidence where it is unsure if it can make a sound or fully informed decision without it.[275]

2.140          However, with the new defence of diminished responsibility,[276] mental health issues will no longer be considered so clear cut in determining liability. The evidence of medical experts on the mental state of the accused will therefore no doubt attract a renewed significance and will in the future, it is submitted, be more readily admitted in this regard.

2.141          The Commission notes that the language used in the Criminal Law (Insanity) Act 2006 refers to “mental disorder” [277] which differs from the English “abnormality of the mind.”[278] Although it remains to be seen how the Irish courts will interpret this provision, it could be considered that the Irish provisions have a much narrower ambit than the corresponding English provision. It can thus be argued that “mental disorder” should be equated with a recognised mental condition, about which expert testimony will undoubtedly be held to be admissible.  

2.142          In its Consultation Paper on Child Sexual Abuse, the Commission considered whether or not expert evidence should be considered admissible in helping to determine the credibility of alleged victims of child sexual abuse.[279] The Commission recognised that matters of human nature and behaviour within the limits of normality are not susceptible to expert evidence.[280]

2.143          The Commission went on to refer to a number of English cases where expert evidence on matters such as credibility of the accused,[281] and the credibility of the accused’s allegation of assault,[282] but recognised that the “child sexual abuse syndrome” as [at the time of the report] lacks clear scientific empirical validation.”[283]

2.144          The Commission outlined both the advantages, such as giving the jury a more informed perspective, and explaining the reasons for a child’s unusual behaviour, and disadvantages, such as the possibility of usurpation of the role of the finder of fact and delay, of admitting evidence on the likely reactions of child victims of sexual abuse.[284]

2.145          In conclusion, the Commission provisionally recommended that expert evidence be admissible as to competence and as to children's typical behavioural and emotional reactions to sexual abuse, a recommendation that was confirmed in the later Report.[285]

2.146          The Commission’s recommendations on this issue reflect the general trend of the courts to adapt to new and emerging forms of expertise, and a willingness to take a flexible approach in relation to what can be considered an issue that is not within the common knowledge of the finder of fact and on which expert evidence is therefore considered beneficial and admissible.

(ii)           England

2.147          The courts have readily allowed expert evidence to prove recognised mental illness, however recent cases in England show that the categories of what will be considered ‘mental illness’ have expanded over the years and evidence is now being allowed in a far wider range of cases than anticipated by Turner.

2.148          For example in R v Toner[286] expert evidence showing that a mild hypoglycaemic attack could have negatived intent was allowed. Similarly in R v Ward[287] psychological evidence was allowed to help prove that the accused was suffering, while not from a mental illness, from a personality disorder so serious as to be described as a mental disorder.

2.149          Expert evidence has also been admitted in England in cases involving inter alia insanity,[288] battered wives syndrome,[289] and automatism.[290] It has also been accepted that expert psychiatric evidence is legally necessary where examining the issue of diminished responsibility.[291]

2.150          In R v O'Brien[292] a similarly broader approach to the admissibility of expert psychiatric evidence was taken. Roche LJ stated:

“At one time the law was thought to be that expert evidence of the kind that we have heard could only be admitted if that evidence showed a recognised mental illness, this being the interpretation placed upon R. v. Turner. It has now been accepted that expert evidence is admissible if it demonstrates some form of abnormality relevant to the reliability of a defendant’s confession or evidence.” [293]

(iii)              Australia

2.151          It is also interesting to note that in the Australian case Murphy v The Queen[294], the High Court of Australia reversed the decision of the trial judge that the evidence of a consultant psychiatrist, which sought to show that the defendant was of limited intellectual capacity, was inadmissible due to the fact that it related to matters of human nature and behaviour within the limits of normality and thus did not qualify as expert evidence.

2.152          In the course of the judgment, the High Court of Australia expressed doubt concerning the English Turner decision:

“Lawton L.J. added some remarks which may not be so unquestionable: “Jurors do not need psychiatrists to tell them how ordinary folk who are not suffering from any mental illness are likely to react to the stresses and strains of life.” There are difficulties with such a statement.  To begin with, it assumes that “ordinary” or “normal” has some clearly understood meaning and, as a corollary, that the distinction between normal and abnormal is well recognized.  Further, it assumes that the commonsense of jurors is an adequate guide to the conduct of people who are “normal” even though they may suffer from some relevant disability.  And it assumes that the expertise of psychiatrists (or, in the present case, psychologists) extends only to those who are “abnormal.”  None of these assumptions will stand close scrutiny.”[295]

2.153          The High Court of Australia then reformulated the test to one that considers whether the evidence would provide assistance to the decision maker.

(c)                Abolition of the Common Knowledge Rule

2.154          As evident from the inconsistent case law, and more obviously from the Australian decision Murphy v The Queen,[296] there appears to have been a shift away from a strict application of the common knowledge rule. Indeed, some jurisdictions have decided to abolish the rule outright.

(i)                 Australia

2.155          The Australian Law Reform Commission’s Interim Paper on Evidence criticised the common law rule for a number of reasons. The Commission argued that what is ‘common knowledge’ must be clearly definable in order for the exclusionary rule to function properly, and that finding a clear definition is however, not possible. [297]

2.156           The Commission also argued that the rule excluding matters of common knowledge lacked theoretical justification because there are many situations in which the trier of fact might have some acquaintance with a subject as would the public at large, but might still find assistance from an expert of some value. [298] They gave the example of evidence that may be given by mental health professions on the ‘ordinary man,’ which as a consequence of the common knowledge rule, will be excluded.

“As a result the common knowledge concept has denied the courts…..the work done by psychologists in conducting research into perception, memory, narration and in demonstrating the fallibilities of eye witness identification and the giving of confessions. A refusal by the courts to utilise the fruits of such research means that they base their decisions on knowledge that is incomplete and out of date.” [299]

2.157          The ALRC recommended that, rather than ask whether the area in relation to which expert opinion evidence is tendered is one of common knowledge, the question for the court should be whether the trier of fact could usefully receive assistance from the expert opinion evidence.” [300]

2.158          Following these recommendations, Section 80(b) of the Evidence Act 1995 (Cth) abolished the common knowledge rule excluding expertise being admitted on areas of common knowledge.[301]

2.159          More recently, the Australian, New South Wales and Victorian Law Reform Commissions published a Report on Uniform Evidence Law, [302] which sought to conduct an inquiry into the operation of the laws of evidence in the various jurisdictions. This report addressed whether there was a need to amend Section 80 (b) of the Evidence Act 1995 which removed the exclusionary rule against matters of common knowledge. 

2.160          In the ALRC’s Issues Paper for this report, it was acknowledged that as a result of the abolition of the common knowledge rule, dealing with evidence about such matters as motor vehicle accident reconstruction, which may have been excluded by the application of the common law rules, involves unnecessary time and expense. [303]

2.161          It was further acknowledged in the issues paper that the abolition of the exclusionary rule greatly facilitated the routine admission of expert opinion evidence in relation to identification, which could have the effect of lengthening cases where identification is a main issue. [304]

2.162          In the Final Report of the combined Commissions, it was noted that several submissions had recommended the reintroduction of the common knowledge rule. It was argued by the Law Institute of Victoria that it created a “high risk that juries might rely on, or afford particular probative value to, expert evidence on matters of common knowledge”[305]

2.163          Other submissions received by the Commissions argued that the common knowledge rule prevents difficulties arising where a jury gives undue weight to the opinion an expert who strays outside his or her area of expertise.[306]

2.164          However, the combined Commissions concluded that there was no need to reintroduce the common knowledge rule. They argued that the mere existence of the common knowledge rule is not itself preventive of the problem of experts straying outside their field of expertise. They further argued that there are sufficient safeguards contained within the Evidence Act 1995 to counteract the difficulties created by the abolition of the rule.

2.165          For example Section 55(1) requires any evidence tendered to have the ability to “rationally affect (directly or indirectly) the assessment of the probability of the existence of a fact in issue in the proceeding.” Therefore an opinion based excessively on matters of common knowledge may be excluded as a result of this section.

2.166          Similarly, section 7, which outlines the general admissibility criteria for expert evidence, requires such evidence to be “wholly or substantially” based on expert knowledge, which would appear to exclude evidence predominantly based on matters of common knowledge.

2.167          Furthermore, section 135 gives the court a general discretion to exclude evidence likely to; be unfairly prejudicial to a party; be misleading or confusing; or cause undue waste of time.

2.168          These provisions, in the Commissions view, along with the benefits of the abolition of the common knowledge rule, are sufficient reasons not to reintroduce the rule.[307]

(ii)               New Zealand

2.169          In its discussion paper on Expert Evidence and Opinion Evidence[308] the New Zealand Law Reform Commission considered the common knowledge rule and the desirability of its retention.

2.170          The Commission explained that the primary justification for preventing an expert from giving evidence on a matter within the knowledge of the finder of fact is that “to allow expert evidence in such a case would be to defeat the purpose for which juries are used.”[309]

2.171          However, the Commission also expressed the view that the rule can “operate to limit unduly the reception of evidence which would add to the understanding and knowledge of the judge or jury” because of the fact that it “excludes evidence by its subject matter without regard to its reliability and value in the trial.”[310]

2.172          As a result of these findings, the Commission recommended the abolition of the common knowledge rule and outlined two main alternatives for reform based on recommendations of other Law Reform Commissions. However, the Commission also acknowledged that both options would have the same substantive effect and would exclude the same evidence on the same grounds.

2.173          First, the Australian approach, which allows expert opinion wholly or substantially based on specialised knowledge, but subject to a general exclusionary power for quality control. Second, the Federal Rules of Evidence approach, which allows such expert opinion evidence as would “assist the trier of fact to understand the evidence or to determine a fact in issue,” subject to a general exclusionary power.[311]

2.174          In its final Report on Evidence – Reform of the Law, the New Zealand Law Commission considered these options for reform and concluded that the ‘common knowledge’ and ‘ultimate issue’ rules should be abolished, and that they should be replaced by a ‘substantial helpfulness’ test. This would allow opinion evidence if the opinion is likely to “substantially help” the court or jury to understand other evidence or ascertain any material fact.[312]

2.175          The Evidence Act 2006[313] has taken on board these recommendations. Section 25 (1) now provides that:

“An opinion by an expert that is part of expert evidence offered in a proceeding is admissible if the fact-finder is likely to obtain substantial help from the opinion in understanding other evidence in the proceeding or in ascertaining any fact that is of consequence to the determination of the proceeding.”

2.176          Section 25 (2) (b) further provides that an opinion by an expert is not inadmissible simply because it is about a matter of common knowledge.

(d)               Conclusion – Is Reform of the Common Knowledge Rule Necessary?

2.177          As already discussed, the common law rule against permitting expert evidence on matters of common knowledge remains firmly applied in this jurisdiction. However, recent case law also reveals an increasing willingness on the part of the courts to expand the interpretation of what consists of matters outside the scope of knowledge of the finder of fact and the boundaries of expertise continues to expand.

(i)                 Abolition of Common Knowledge Rule

2.178          It is open to the Commission to recommend following the approach taken in jurisdictions such as Australia and New Zealand, namely the adoption of a rule whereby expert evidence will not be excluded solely on the grounds that it is based on a matter of common knowledge.

2.179          The Commission could recommend a new test for admissibility, modelled on the New Zealand provisions, which takes a functional approach and requires consideration about whether the trier of fact could usefully receive assistance from the expert opinion evidence.  

2.180          This general test could be balanced by provisions such as those contained in Australian legislation which give the court a general discretion to exclude evidence likely to; be unfairly prejudicial to a party; be misleading or confusing; or cause undue waste of time.

2.181          The possible advantages of such a reform have been detailed above. It can be argued that there are many issues which can be considered within the common knowledge of the court but on which expert evidence would still be of extreme benefit to the finder of fact.

2.182          It can be also argued that the case law demonstrates that the rule continues to be inconsistently applied, and the courts have continuously circumvented it, to the extent that it has become extinct in all but name. Its express abolition would therefore not have significant practical ramifications.

2.183          Such a reform would therefore significantly widen the scope of admissible expert evidence. However, it could be considered that this is a trend that is occurring in the case law regardless as the courts appear to be giving an increasingly broad interpretation to what is outside of the scope of knowledge of the finder of fact.

(ii)               Retention of Common Knowledge Rule

2.184          A strong argument can also be made for the retention of the common knowledge rule. It is acknowledged that the rule helps to clarify for both the court and any potential experts for the parties to the case what the precise scope of expert evidence that will be permitted encompasses.

2.185          It further helps to consolidate in the expert’s mind that his or her role is to give expert evidence and not to act as an additional finder of fact giving his or her view on the issues in the case as this amounts to a usurpation of the role of the finder of fact.

2.186          The rule also requires the expert to prove to a high standard that the evidence they are giving involves ‘expertise,’ and also requires the expert to ensure that  his or her evidence does not stray outside the area of expertise. Therefore the rule promotes a high standard of expert testimony.

2.187          It has already been explained that the abolition of the rule can lead to problems such as undue lengthening of cases as it has the potential to greatly widen the matters for which a party will seek to adduce expert evidence.

2.188          There is also the added danger with the abolition of the rule that where an expert opinion is given on an issue, on which the court would be perfectly entitled to come to their own opinion, undue weight or deference may be given to the opinion of the expert as they may be erroneously considered to be better placed to give an opinion.

2.189          Furthermore, as can be seen in the case law, the rule in practice has not caused any major difficulties as the courts have been willing to circumvent it by stretching the boundaries of what will be considered, on the one hand a matter of common knowledge, and on the other hand, outside the scope of knowledge of the finder of fact.

2.190          The Commission now turns to set out its provisional recommendations on this area. In the view of the Commission, the role serves a valuable purpose in clearly defining the type of expert evidence that will be given, and bearing in mind the fact that expert opinion evidence is in itself a strict exception to the rule against opinion evidence, it should remain strictly applied.

2.191          The Commission further believes that any potential difficulties that may occur with the operation of the rule, such as its ability to exclude evidence that may have strong probative value, will be resolved by the court’s ability to give a flexible interpretation to what consists of matters of common knowledge and the willingness of the court to recognised new areas of expertise.

2.192          The Commission provisionally recommends that the common knowledge rule should not be abolished and that matters of common knowledge should remain outside of the scope of matters on which expert testimony can be given.  

(3)                The Ultimate Issue Rule

2.193          Traditionally, expert opinion evidence about the ultimate issues in the case was not permitted, as this would effectively erode the jury process and be a ‘trial by expert.’[314]

2.194          The underlying rationale behind the exclusionary rule is therefore the desire to prevent the role of the judge or jury from being usurped. Another concern is to prevent the finder of fact from being unduly influenced by an expert opinion, which may not be reliable, on an issue which is crucial to the ultimate decision in the case.

2.195          However, recent cases reveal that this rule is now gradually being perceived as being unduly restrictive. Furthermore, the courts have always had difficulties in defining what constitutes the ultimate issue. This has led to different interpretations being given to the rule. As a result, it has been increasingly abandoned or, with careful wording, circumvented, in this jurisdiction, in line with developments in the US, Australasia and Canada, to the extent that it could now be considered almost obsolete.

(a)                Ireland

2.196          The traditional rule against expert evidence on issues which pertain to the ultimate issues in the case can be seen in The People (DPP) v Kehoe.[315] Here, O’Flaherty J felt that the expert psychiatrist had “overstepped the mark” when he expressed an opinion that the accused did not have an intention to kill and that the accused was telling the truth.

2.197          This was a murder case and the issue for the court was to decide whether the accused could avail of the defence of provocation. In expressing an opinion that the accused did not have an intention to kill, the expert was clearly trespassing on the duty of the jury to decide on provocation.

2.198          However, a more flexible approach can be seen in later cases where the courts have recognised that a strict application of the exclusionary rule is not always appropriate. For example, Barron J. in McMullen v Farrell[316] stated a belief that there are certain cases where professional witnesses are entitled to express their opinion on the question which the court has to decide.

2.199          This development is not unremarkable as a considerable body of inconsistent case law was generated by the rule.[317] This inconsistency of application can be explained by recognising that the reason for adducing expert evidence was that the finder of fact did not have the expertise on which to base a decision.

2.200          One area where the ultimate issue rule has often been raised is in the context of nullity proceedings. In many such cases a medical inspector will be appointed to consider whether both parties had the mental capacity to enter into the marriage, a question which essentially amounts to the ultimate issue in the case. This fact was acknowledged by Budd J in S(J) v S(C)[318]

“In some unopposed nullity cases, the Consultant Psychiatrist gives an opinion verging on the ultimate issue which the Court is going to have to decide, namely, whether one or other of the parties suffered from such illness at the time of the ceremony of marriage as to be incapable of entering into and sustaining a viable marital relationship.”[319]

2.201          However, it can be argued that the role of the medical inspector in such cases is not decisive of the issues. Although the medical inspector will give an opinion about whether or not, in his or her expert view, the individual was mentally capable of entering into a viable marriage at the time of the marriage, it remains the role of the court to decide whether or not to grant the annulment. Although the court will take the expert’s evidence into account this is not binding and it is open to the court to reject or place little weight to the evidence and grant a decision that is not reflective of the expert’s evidence. 

2.202          Furthermore, despite the decline in the ultimate issue rule in Irish case law, the courts are very careful to avoid experts making widespread findings of fact, and it has been stressed in several cases that the judge cannot abdicate his role to the expert, no matter how distinguished.[320]

(b)               England

2.203          The common law rule has been similarly eroded in England. It has been statutorily abolished in the context of civil law proceedings, but despite calls for reform, continues to have application in the context of criminal proceedings.

(i)                 Civil Proceedings

2.204          In its 17th Report Evidence of Opinion and Expert Evidence the English Law Reform Committee expressed the opinion that in certain cases, the opinion of an expert on an issue in the proceedings can be a useful aid to the judge who has to decide the case and thus the Committee saw “no reason why an expert witness should not be asked the direct question as to his opinion on an issue in the action which lies within the field of his expertise.”[321]

2.205          Pursuant to the recommendations of the Law Reform Committee, the Civil Evidence Act 1972 gave express statutory permission for the giving of evidence on an ultimate issue. Section 3 of the Act provides:

“(1) Subject to any rules of court made in pursuance of Part I of the Civil Evidence Act 1968 or this Act, where a person is called as a witness in any civil proceedings, his opinion on any relevant matter on which he is qualified to give expert evidence shall be admissible in evidence

 (3)In this section "relevant matter" includes an issue in the proceedings in question.”

2.206          Notwithstanding this generality however, Section 5(3) of the Act qualifies this general permission by giving the court the general discretion to exclude any evidence it so wishes.  

2.207          In English civil cases therefore, evidence on an ultimate issue can be admitted, but equally it can be prohibited where, in the opinion of the court, it is not relevant or has little or no probative value, or where the court finds for whatever reason it should not be admitted.

(ii)               Criminal Proceedings

2.208          In criminal proceedings, the traditional strict application of the ultimate issue rule has been replaced by a more flexible approach; however, the rule continues to apply.

2.209          In DPP v A and BC Chewing Gum Ltd.[322] evidence of child psychologists was excluded in a case involving a charge of contravening the Obscene Publications Act 1959 by publishing bubble gum battle cards which, it was alleged, were of an obscene nature. On appeal, the question was raised if it had been appropriate to exclude the evidence for reasons that it was evidence on the very issue the court had to determine – i.e. if the cards were of an obscene nature.

2.210          The court drew a distinction between questions about the effect literature, purported to be of an obscene nature, would have on young children, and the question of whether the literature in question was such “to deprave and corrupt” such children. The second question, they held, was a matter for the court, not due to the fact that it amounted to an ultimate issue in the case, but due to the fact that such a question was not outside the range of scope and knowledge of the ordinary person.

2.211          In the course of the judgment, however, Parker C.J. alluded to the general degeneration of the ultimate issue rule:

“With the advance of science more and more inroads have been made into the old common law principles. Those who practise in the criminal courts see every day cases of experts being called on the question of diminished responsibility, and although technically the final question ‘Do you think he was suffering from diminished responsibility’ is strictly inadmissible, it is allowed time and time again without any objection.”[323]

2.212          More recently, in R v Stockwell[324] Taylor J expressly stated that the ultimate issue rule has been effectively abolished in criminal cases in England:[325]

“The rationale behind the supposed prohibition is that the expert should not usurp the functions of the jury. But since counsel can bring the witness so close to opining on the ultimate issue that the inference as to his view is obvious, the rule can only be, as the authors of the last work referred to say, a matter of form rather than substance. In our view an expert is called to give his opinion and he should be allowed to do so. It is, however, important that the judge should make clear to the jury that they are not bound by the expert’s opinion, and that the issue is for them to decide.”[326]

2.213          It is arguable, however, that despite the near eradication of the ultimate issue rule in England, many of the older cases where evidence on the ultimate issue was excluded would still have the same result, if not on the same grounds, if decided today.

2.214          This is because the other admissibility rules, for example the requirement that the issue is one that is outside the knowledge and expertise of the court, will still apply to exclude evidence that is not considered necessary as a result of the court’s determination not to let the role of judge and jury be usurped by expert witnesses. This is well demonstrated by the decision of the court in DPP v A and BC Chewing Gum Ltd.[327]

2.215          Another example of this approach can be seen in R v Ugoh.[328] This was a group rape case where expert evidence from a psycho-pharmacologist was admitted to the extent that the expert could state the likely effects of alcohol on the complainant’s capacity to consent to sexual intercourse and to explain how the complainant was likely to act with the quantity of alcohol in her blood stream, both of which were issues in the case.

2.216          However the expert was not allowed to give evidence on the issue of whether or not the complainant’s capacity to consent would have been evident to those who were with her at the time. The court did not object to the evidence due to the fact that it went to an ultimate issue in the case. It did object due to the fact that the accused’s ability or inability to appreciate the complainant’s inability to consent was not an issue for which expert evidence was necessary, as this was not outside the scope of knowledge of the jury.

“The appellants were normal young men, not themselves under the influence of drink or drugs, whose ability or inability to appreciate the complainant’s inability to consent were a matter for the jury to assess. Their age, inexperience, tiredness or desires at 3.00 a.m. on a Saturday night or early Sunday morning were all matters for the jury to assess.”[329]

2.217          As can be seen from this case law, despite uncertainty relating to the extent of the application of the ultimate issue rule in English criminal proceedings, the English courts have retained a wariness to admit any expert evidence that may unduly encroach on the role and function of the judge or jury, regardless of the rule used to prohibit this evidence.

(c)                Australia

2.218          In its 1985 Interim Report on Evidence the Australian Law Reform Commission recognised that the ultimate issue rule has been repeatedly criticised by numerous Law Commissions. [330]

2.219          They also point out that there have been inconsistencies in the correct formulation and application of the rule and that “the courts have departed from the most commonly understood version of the rule when they have felt it appropriate, resulting in an ad hoc development of the law.”[331]

2.220         The Commission further argued that the underlying rationale for the rule, namely the assumption that the role of the finder of fact would be usurped without it, is erroneous because such an assumption is founded on a misunderstanding of the role and function of witnesses, whose task it is to present the evidence, and that of judges and juries, whose task it is to evaluate this evidence. [332]

“The popular justification for the rule, that it prevented the expert or lay witness from usurping the function of the jury, is misconceived. There is no usurpation. The jury, in any event will be told that they must assess the evidence, lay and expert. It is upon the most important issues that expert assistance can be crucial and the courts need to be able to receive it. It is necessary to give both sides, be the proceedings criminal or civil, full opportunities to call witnesses to give relevant evidence.”[333]

2.221          The Commission therefore opted to concur with the approach of the United States Federal Rules of Evidence and with the recommendations of Law Reform Commissions in Canada,[334] Scotland[335] and South Australia,[336] that the ultimate issue rule be abolished

2.222          With the introduction of the Evidence Act 1995 (Cth) the common law rule against expert evidence going to the ultimate issue was removed by Section 80. In its Issues Paper on Evidence, the Australian Law Reform Commission examined the operation of section 80. [337]

2.223          The Commission acknowledged that the removal of the rule had led to problems in certain categories of cases, such as professional negligence cases, where concern was raised that juries in such cases may be overly influenced by expert evidence on the central issue involved, i.e. whether or not the defendant has been negligent.[338] They also noted that there have been several calls for the revival of the rule, based on concerns about the effect of such evidence on a jury.[339]

2.224          These arguments were revisited in the Final Report on Uniform Evidence law, where the combined commissions considered whether or not there is a need for the revival of the rule.[340] The Commission highlighted the many submissions that had been made in support of the rule but ultimately came to the conclusion that the uniform Evidence Acts seem to be operating satisfactorily without the rule and so recommended that the ultimate issue rule remain abolished and that it should not be reintroduced.[341]

(d)               New Zealand

2.225          In the New Zealand case R v Howe[342] the Court of Appeal referred to the general trend of a move away from a strict application of the ultimate issue rule;

“The rule that a witness cannot give evidence on the ultimate issue has now been very much eroded. Experts do commonly give evidence on matters on which the ultimate decision in the case turns.”[343]

2.226          The rule and the desirability of its retention was also the subject of consideration in the discussion paper on Expert Evidence and Opinion Evidence of the New Zealand Law Reform Commission.[344] The Commission acknowledged that in practice the rule has proved to be too restrictive and tends to be widely ignored.[345]

2.227          The Commission acknowledged that the rationale behind the rule is the danger that the fact finder will be over-impressed by unreliable opinion and give it weight which it does not deserve.

2.228          However, the Commission expressed the view that this danger is present regardless of whether the evidence is directed at an ultimate issue or not, and therefore a more appropriate approach is to assess any evidence directly “the primary issue being whether the evidence is helpful and reliable, not whether it goes to the ultimate issue.”[346] This recommendation was approved in the New Zealand Law Reform Commission’s Final Report on Evidence.[347]

2.229          The Commission’s recommendations were implemented in the New Zealand Evidence Act 2006. Section 25(2)(a) provides that an opinion of an expert is not inadmissible because it is about an ultimate issue to be determined in the proceedings. 

2.230          Expert evidence on an ultimate issue in a case is therefore statutorily admissible in both criminal and civil proceedings in New Zealand.

(e)                Conclusion - Is Reform of the Ultimate Issue Rule Necessary?

2.231          As already discussed, the ultimate issue rule against permitting expert evidence on matters which go to the ultimate issue in a case remains firmly applied in this jurisdiction.

2.232          However, recent case law also reveals difficulties with the rule such as inconsistent interpretation and application. This has led many jurisdictions to expressly abolish the ultimate issue rule.

(i)                 Abolition of the Ultimate Issue Rule

2.233          It has been argued that the underlying basis for the rule, namely the usurpation of the role of the jury, does not in fact require the rule. It remains the function of the jury to accept or reject the opinion of the expert and thus to decide on the ultimate issue; merely hearing the expert’s opinion evidence on the ultimate issue does not amount to the expert having the final say.

2.234          It is open to the Commission to recommend the abolition of the ultimate issue rule and its replacement with a general admissibility test based on whether or not the evidence is of assistance to the court, whilst at the same time emphasising the informative and discretionary rather than binding nature of the expert’s opinion, and the ultimate duty of the finder of fact to decide the case.

2.235          Such a reform would remove the inconsistencies and barriers imposed by the rule and ensure that the judge or jury have all necessary expertise available to them on every issue involved in the case.

(ii)               Retention of the Ultimate Issue Rule

2.236          There is also a valid argument to be made in favour of the retention of the ultimate issue rule. The argument can be made that if “ultimate issue” is properly interpreted, by its very definition expert evidence would never be permitted or considered necessary.

2.237          Expert evidence is often necessary to explain to the judge or jury the scientific or technical background of issues that are central in a case. However, the role of the expert in such cases is not decisive of the issues.

2.238          The overriding function of expert testimony is to provide the finder of fact with the necessary expert knowledge to come to their final conclusions. The overriding function of the finder of fact is to use the expert information given to them and then come to its own informed conclusions about the ultimate issue involved in the case.

2.239          Although the court will take the expert’s evidence into account, this is not binding and it is open to the court to reject or place little weight on the evidence and to give a decision that does not reflect the expert’s evidence. 

2.240          This interpretation of the ultimate issue rule endorses both the underlying roles of the expert witness and of the judge and / or jury. The ultimate issue rule should this be considered as prohibiting an expert from giving an opinion if to do so would involve unstated assumptions as to either disputed facts or propositions of law.[348]

2.241          The retention of the rule in principle is important, provided that the court is left with the discretion to allow such evidence in a particular case where necessary.  The Commission is of the view that the rule serves the valuable purpose of strengthening the role of the finder of fact by ensuring that the expert witness does not usurp the role of the court to determine the issues in a case. It is also a useful benchmark for the expert witness to ensure that he or she does not step over the line in relation to the evidence that is permissible and stray outside the area of expertise for which expert testimony is being adduced.

2.242          The Commission provisionally recommends that the Ultimate Issue rule should not be abolished and should have continued application as it does not impose any excessive difficulties in practice.

2.243          The Commission provisionally recommends that the Court should continue to be entitled to allow expert evidence to inform and educate the judge and or jury about the background to the ultimate issue where necessary, whilst emphasising that the ultimate decision on such issues is for the court and not the expert.

(4)                Expert and Non-Expert Evidence of Fact

2.244          As recognised above, expert witnesses can often give expert evidence of fact as well as expressing their opinion, such as where certain results or techniques require expertise to explain. Furthermore, the distinction between expert and non-expert evidence of fact can, in reality, have significant ramifications. For example, the costs of an expert witness may be recovered whereas those of a witness of fact may not. Similarly, while both witnesses of fact and expert witnesses are equally legally compellable, it is rarely the case in practice that the court will be called on to compel the attendance of an expert witness, as generally a party will have a number of possible experts on a particular issue to choose from, and it is clear that a reluctant or unwilling expert is likely to do more harm than good to the party’s case.[349]

2.245          In the 1843 decision of Webb v Page[350] Maule J set out a clear definition of the distinctions between witnesses who are called to give evidence of fact on facts which they have seen, and those expert witnesses who are called to give evidence of fact on facts of which he is knowledgeable as a result of experience or study in the field of expertise:

“There is a distinction between the case of a man who sees a fact and is called to prove it in a Court of Justice, and that of a man who is selected by a party to give his opinion on a matter with which he is peculiarly conversant from the nature of his employment in life. The former is bound, as a matter of public duty, to speak to a fact which happens to have fall within his knowledge – without such testimony the court of justice must be stopped. The latter is under no such obligation. There is no necessity for his evidence, and the party who selects him must pay him.”[351]

2.246          More recently, however, the distinction between the two is not always clear cut, and several cases have had trouble distinguishing between expert and non-expert evidence of fact.[352] For example in The People (DPP) v Buckley[353] the question arose whether the defendant’s admission that the substance recovered from his pocket was cannabis was sufficient evidence that it was cannabis in the absence of a certificate of analysis from the Garda Forensic Science Laboratory confirming that it was such.

2.247          Charleton J relied on the decisions in R v Chatwood[354] and Bird v Adams[355] in ruling that “the qualities of cannabis are not now so unusual as to put it in a different category so that expert evidence of its presence is always required.”[356] Charleton J appeared to be of the opinion that the defendant could give factual evidence that the substance he had in his possession was cannabis. “An accused, who admits a substance is cannabis can be, but not necessarily must be, relied on to know what he is talking about.”[357]

2.248          In Bird v Adams[358] the English High Court pointed out that:

 “…there are many instances where an admission made by a defendant on a matter of law in respect of which he was not an expert was really no admission at all, e.g., a defendant could not know in a bigamy case whether a foreign marriage was valid…but here the…defendant certainly had sufficient knowledge of the circumstances of his conduct to make his admission at least prima facie evidence of its truth.”

2.249          This decision was relied on in R v Chatwood[359] where a heroin addict’s confession that he had injected heroin was sufficient evidence to prove that the substance in question was heroin. The Court of Appeal appeared to characterise the admission as expert opinion evidence, but Hodgkinson & James argue that there is no real difference between the classic definition of lay witness evidence as evidence perceived by the senses, and the evidence given in this case. They consider that the court may have been misled due to the fact that a heroin rush is not perceived by one of the five senses when injected, but nevertheless that the admission should have been considered as evidence of fact.[360]

2.250          These cases highlight that the lines between expert and non-expert opinion evidence of fact are often blurred, particularly where narcotics cases are involved. However it would appear from the foregoing that the courts are willing to admit the evidence as evidence of fact, as it will remain open to the trier of fact to decide on the value or lack thereof to attach to such evidence.

2.251          The Commission believes that this is an important requirement as if it is unclear, greater evidential weight may be given if it appears that the expert is stating a fact, rather than his or her own opinion.

2.252          The Commission provisionally recommends that experts should be required, as far as possible, to distinguish clearly between matters of fact and matters of opinion when giving their expert evidence both orally and in the expert report.

(5)                Non-Expert Opinion Evidence

2.253          Dickson J in R v Abbey[361] clearly elucidated one of the reasons for the extent of the categories of expert evidence:

“The law of evidence…reposes on a few general principles riddled by innumerable exceptions.”

(i)                 Common Law Exceptions to the Rule against Opinion Evidence

2.254          In keeping with this, a number of common law derogations from the exclusionary rule outside of expert testimony can be seen.

(I)                 Where Fact and Inference are Indivisible

2.255          For example non-expert opinion evidence may be admitted where it is necessary to do so because of the indivisibility of fact and inference in a witness’ testimony. As explained by Mac Dermott LCJ in Sherrard v Jacob,[362] there may be:

 “…instances in which the primary facts and the inference to be drawn there from are so adherent or closely associated that it may be hard, if not impossible, to separate them.”

(II)                Matters of Common Experience

2.256          The exclusionary rule may also be relaxed where the matter is within “common experience within the ken of ordinary men,”[363] for example an observation on someone’s state of mind at a particular time.

(III)              Matters Incapable of Precise Appreciation

2.257          An exception may also be made where the matter is one that is not capable of exact observation and the most that can be expected is an approximation or estimation, for example evidence of identification, “the speed of a motor car, the size of a crowd, the temperature of a day, and any question of measurement.”[364]

(IV)              Catch-All Exception where Convenient to Do So

2.258          Finally, there is a broad, catch-all range of circumstances where witnesses are permitted to give opinions where this is convenient and the opinion does not go to the facts of the case. As Lavery J stated in AG (Ruddy) v Kenny: [365]

“…there are innumerable incidents of everyday life upon which an ordinary person can express a useful opinion and one which ought to be admitted.”

2.259          In this case, the ‘incident’ in question was drunkenness, which, in the view of the learned judge, was a matter on which an ordinary person was capable of expressing an opinion, without the need of the expert opinion of a member of An Garda Siochana or a medical expert.

(ii)               Statutory Exceptions to the Rule against Opinion Evidence

2.260          A number of statutory exceptions have also developed over time. Section 3(2) of the Offences against the State Act (Amendment) Act 1972[366] provides that where certain members of the Garda Siochana testify in evidence that ‘he believes that the accused was at a material time a member of an unlawful organisation,’ then this statement constitutes evidence that the accused was then such a member.

2.261          Other statutory provisions which permit express opinions to be adduced in evidence include the Proceeds of Crime Act 1996,[367] the Domestic Violence Act 1996[368] and the Competition Act 2002.[369]

E                  The Weight and Value to be Attached to Expert Evidence

2.262          As will be discussed below, the general approach of the courts is that reliability of expert evidence is a matter to be assessed at the weight, rather than admissibility, stage of litigation. Whereas the court might be willing to admit expert evidence freely, such a favourable view may not always be taken when assessing the weight to be attached to such evidence.

(1)                The Court Assesses the Value of the Expert Evidence

2.263          It is important to note that the court is not obliged to accept or act on expert evidence and can refuse to admit it or reject it if they so wish. The decision making function of the court must not be usurped by the expert, and it remains at all times the duty of the court to determine the truth of the matter at hand. The evidence of an expert will therefore only be of persuasive, not binding effect, to be taken into account along with all of the other evidence in the case.  

2.264          This was acknowledged by the court in Davie v Edinburgh Magistrates[370] where the court rejected the defender’s contention that the court was bound to accept the evidence of their main expert witness as no similar expert had been adduced by the pursuer to counter his conclusions. Although Lord President Cooper acknowledged the fact that the expert’s opinion was uncontested, however, he went on to state:

“Expert witnesses, however skilled and eminent, can give no more than evidence. They cannot usurp the functions of the jury or Judge sitting as a jury……The scientific opinion evidence, if intelligible, convincing and tested, becomes a factor (and often an important factor) for consideration along with the whole other evidence in the case, but the decision is for the Judge or jury.”[371]

(2)                The Evidence of Lay Witnesses can be given Greater Weight than Expert Evidence

2.265          In this jurisdiction it has long been recognised that the court is entitled to prefer the evidence of lay witnesses over experts if this appears to fit in better with the facts of the case. In Poynton v Poynton[372] the court held that where two witnesses were advanced in support of a case, one being a witness of fact who had personally perceived the event, and one being an expert witness who expressed an opinion on the issue in question (in this case the sanity of a testator) the evidence of the witness of fact is to be preferred. Madden J reasoned:

“We have the highest authority for the proposition that mere speculative opinion and expressions of opinion cannot reasonably be compared with the evidence of witnesses who had an opportunity of applying the ordinary facts of mental capacity….in my opinion the evidence given on behalf of the plaintiff (supporting the will) runs on a different plane from the purely speculative evidence, unaccompanied by any attempt to test the mental capacity of the testator which was relied on by the defendant, and that the jury acted unreasonably in not differentiating between the two classes of evidence.”

2.266          This judgment would appear to hold that where a witness of fact and an expert witness are presenting conflicting evidence, the testimony of the witness of fact is to be afforded greater weight. However, it is also evident from this judgment that the expert witness was criticised for his failure to make a thorough investigation of the testator.

2.267          In circumstances where the expert has presented a well researched and thorough argument, particularly where the opinion relates to issues of medical expertise, it can be argued that the opinion of any expert may in some cases be of far more benefit than the unlearned opinion of a witness of fact. However, there are a number of cases in this jurisdiction where lay evidence was accorded higher weight than expert evidence, which demonstrates that the courts continue to place a high value on the testimony of lay witnesses.

2.268          For example, the Supreme Court in Hanrahan v Merck, Sharpe & Dohme Ltd,[373] agreed with the plaintiff’s contention that “there is greater force and credibility to be given to the first-hand evidence of witnesses whose truthfulness was not called into question, as opposed to the largely abstract ex post facto evidence of scientists who had no direct or personal experience of the matters complained of.”[374]

2.269           There are also a number of examples of the Court preferring the evidence of lay witnesses over scientific testimony in criminal cases where experts are advanced in support of a defence of insanity to a murder charge. For example in both The People (AG) v Fennell (No. 1) [375] and The People (AG) v Kelly[376] the jury preferred lay testimony which supported the proposition that the accused was sane at the time of the fatal attack. On appeal, the Court in both cases stressed that the jury were perfectly entitled to do so.

2.270          A series of nullity cases also demonstrate that the courts are quick to prefer their own opinion over that of an expert where they believe this is most appropriate and so attach little value to the expert’s opinion.[377] This highlights that the courts are wary prevent a situation of ‘trial by expert’ and will not attach high or excessive weight to an expert’s opinion if the opinion of the court, having heard all of the evidence, does not correspond.

(3)                Factors to be Taken into Account When Determining Weight

2.271          A number of cases have discussed the range of factors to be taken into account when determining the appropriate weight to attach to any expert evidence. In this jurisdiction in AG (Ruddy) v Kenny,[378] Davitt P outlined some of the factors need to be taken into account to determine the weight to be given to such evidence:

 “It will depend upon the nature of the evidence, the impartiality of the witness and his freedom from bias, the facts on which he bases his opinion, and all the other relevant circumstances.”

2.272          Similarly, in the English decision Davie v Edinburgh Magistrates[379] Lord President Cooper held that the value and weight to be attached to expert evidence depends upon:

“…the authority, experience and qualifications of the expert and above all upon the extent upon which his evidence carries conviction and not upon the possibility of producing a second person to echo the sentiments of the first expert witness.”

2.273          However, the main worry is that, despite these guidelines, greater deference will be given to the opinion of an expert whose testimony is eloquent and impressive, but not necessarily very relevant or reliable. The danger that excess weight will be accorded to a particular theory can be heightened when the task of determining weight is given to a lay jury or tribunal with little legal training, regardless of warnings given by a judge in summing up to prevent this.

2.274          In a 1999 survey of Australian judicial perspectives on expert testimony, approximately 70% of judges surveyed conceded that they had had occasions where they had felt that they had not understood expert evidence in the cases before them.  20% of respondent judges said that they “often” experienced difficulty in evaluating opinions expressed by one expert as against those expressed by another.[380]

2.275          This survey reveals a potential difficulty created by the situation where the judge or jury is required to assess the value of evidence that is being admitted for the sole reason that it is considered outside of the scope of knowledge of the judge or jury.

(4)                Conflicting Expert Testimony

2.276          The question of weight also encompasses the issue of conflicting expert evidence. In most litigation, both parties will advance experienced experts to present their own, often contradictory, arguments. The difficulty for the finder of fact to decide on which expert to agree with is apparent when one considers that the reason for adducing the evidence in the first place is the fact that it is outside the range of knowledge of the court.

2.277          Lord Woolf summarised the inherent contradiction within expert evidence well in his Final Report on reform of the English civil justice system, Access to Justice:

“The traditional way of deciding contentious expert issues is for a judge to decide between two contrary views. This is not necessarily the best way of achieving a just result. The judge may not be sure that either side is right, especially if the issues are very technical or fall within an area in which he himself has no expertise. Nevertheless, he hopes to arrive at the right answer. Whether consciously or not his decision may be influenced by factors such as the apparently greater authority of one side's expert, or the experts' relative fluency and persuasiveness in putting across their arguments.” [381]

2.278          This effectively means that in the ‘battle of the experts,’ the opinion given by the witness with the greater oratorical skills may be the one that sways the opinion of the judge or jury, particularly where complex issues are in question, regardless of whether the opinion is the more reliable in the circumstances.

2.279          It was stressed in Best v Wellcome Foundation Ltd.[382] that the function of the court where there is a conflict of evidence is not to decide which witness they prefer. Rather, as Finlay CJ stated:

“The function which the court can and must perform is to apply common sense and a careful understanding of the logic and likelihood of events to conflicting opinions and conflicting theories concerning a matter of this kind.[383]

2.280          This is a reasonable statement; however, it is submitted that, in reality, expert evidence is being advanced more and more frequently on complex subjects and theories. In such instances, applying common sense and logic may not make the task any easier. The inherent difficulty was noted over a century ago by the great American jurist and judge Learned Hand when he explained that:

“But how can the jury judge between two statements each founded upon an experience confessedly foreign in kind to their own? It is just because they are incompetent for such a task that the expert is necessary at all…..If you would get at the truth in such cases, it must be through someone competent to decide.[384]

2.281          More recently in Ireland, O’Sullivan J, writing extra judicially, gave a vivid description of the difficulties he faced in trying a medical negligence case. The task of the judge, he explained, was “to apply the rules of probability to two eminently distinguished and coherent bodies of evidence which were in mutual conflict,” a task which left him feeling like “an intellectual pygmy looking up at two giants: from that vantage point one simply cannot tell which of them is taller.”[385]

F                  Usurpation of the Role of Judge or Jury

2.282          Kenny states that there are three ways in which experts may usurp the role of others in the legal process. They may usurp the function of the jury by giving a conclusion on the ultimate issue in the case rather that providing information to the jury to enable them to reach a more informed conclusion. They may usurp the role of the judge, by imposing on the jury their own interpretation of statutory terms such as ‘responsibility.’ Finally, they may usurp the role of the legislature by giving opinions on general policy in relation to the convictions. For example, “that people who are sick in a certain way should not be sent to prison.”[386]

2.283          Therefore, along with the risk that unwarranted weight will be given to expert evidence, there is also a related and overlapping risk that the opinion of the expert will be taken on board to decide the case at hand, resulting in an effective ‘trial by expert.’ This is particularly so now, since the rule prohibiting the proffering of expert witness opinion on the ultimate issues of a case has been all but abandoned.

2.284          It stands to reason that there is a real risk that a lay jury, and in some cases even experienced judges, might place more emphasis on the opinion given by esteemed experts than on the conclusions that they might draw themselves. It has been repeatedly stressed in the case law that a finder of fact cannot abdicate his or her function to an expert no matter how distinguished.

2.285          For example in R v Turner[387]Lawton J was quite firm in his comments that the courts would be vigilant to prevent ‘trial by psychiatrist’:

“We do not find that prospect attractive and the law does not at present provide for it… we are firmly of the opinion that psychiatry has not yet become a satisfactory substitute for the common sense of juries or magistrates on matters within their experience of life.”[388]

2.286          In this jurisdiction, O’Flaherty J in The People (DPP) v Kehoe,[389] pointed out that the questions as to whether the accused was telling the truth and whether he had an intention to kill were:

 “…clearly matters four-square within the jury’s function and a witness, no more than the trial judge or anyone else, is not entitled to trespass on what is the jury’s function.”[390]

2.287          In The People (DPP) v Yusuf Ali Abdi[391] Hardiman J warned:

“The role of the expert witness is not to supplant the tribunal of fact, be it judge or jury, but to inform the tribunal so that it may come to its own decision. Where there is a conflict of expert evidence it is to be resolved by the jury or by the judge, if sitting without a jury, having regard to the onus of proof and the standard of proof applicable in the particular circumstances. Expert opinion should not be expressed in a form which suggests that the expert is trying to subvert the role of the finder of fact.”

2.288          Similarly, in The People (DPP) v Fox[392] the Court approved of the comments of Lord President Cooper in the Scottish case Davie v Edinburgh Magistrates.[393] This extract has since been cited with approval in a number of cases in this jurisdiction:[394]

“However skilled or eminent, he can give no more than evidence. They cannot usurp the functions of the jury or the judge, sitting as jury, any more than a technical assessor cannot substitute his evidence for the judgment of a court.”

2.289          Related sentiments have been expressed in a series of nullity cases where the courts have recognised that on the one hand, the evidence of psychologists, psychiatrists and social workers is now recognised of being of great importance in dealing with nullity cases, on the other hand however, deciding the marital status of the parties remains the ultimate responsibility of the judge. The function of any expert witness adduced is to help with this task and not to usurp it. For example, Keane J stated in F(Ors C) v C:[395]

“How was the Court to decide what these phrases mean in the context of any particular case? Not certainly by reference to the evidence of psychiatrists; they can, of course, assist the court as to the nature and extent of any mental illness suffered by a spouse, but it is the responsibility of the courts alone and not of psychiatrists, however eminent, to determine whether a decree of nullity should be granted.”

2.290          Similarly, Murphy J stressed in KWT v DAT[396] that:

“…at the end of the day it seems to me that I cannot abdicate my function to the experts, however distinguished, and even though they are, in the present case, in agreement on the point that the parties to marriage did not have an adequate emotional capacity to sustain the relationship of marriage.”[397]

2.291          This point was cited with approval in MCG(P) v F(A) [398] and F(G) v B(J),[399] highlighting the continuing reluctance of the judiciary to pass the responsibility of deciding on essential elements of the case to an expert witness. Budd J stated:

“When it comes to deciding the issues confronting the Court then the buck firmly lands on the desk of the Court and cannot be shifted to the inspector, however experienced and respected the medical inspector may be.”[400]

2.292          In practice however, where the judge is being asked to adjudicate on issues about which he or she is completely inexperienced, and on which he or she is undecided, it stands to reason that considerable deference will be given to witnesses who present themselves as expert in the field, and present convincing and impressive argument, peppered with technical terminology, even if this is not the most accurate representation of the facts in the case.

2.293          Guidance was given about the role and function of an expert witness in the English case of Liddell v Middleton[401] where Stuart-Smith LJ said:

“The function of the expert is to furnish the Judge with the necessary scientific criteria and assistance based upon his special skill and experience not possessed by the ordinary layman to enable the Judge to interpret the factual evidence of the marks on the road, the damage or whatever it may be. What he is not entitled to do is to say in effect "I considered the statements and/or evidence of the witnesses in this case and I conclude from their evidence that the Defendant was going at a certain speed, or that he could have seen the Plaintiff at a certain point.” As this is essentially a job for the jury to decide.

2.294          He went on to consider the particular facts of the case and concluded in this way:

"We do not have trial by expert in this country; we have trial by Judge. In my judgment, the expert witnesses contributed nothing to the trial in this case except expense. For the reasons I have indicated, their evidence was largely if not wholly irrelevant and inadmissible. Counsel on each side of the trial succumbed to the temptation of cross-examining them on their opinion, thereby lengthening and complicating a simple case.

G                  Junk Science and the Need for a Reliability Test

2.295          Testing the reliability of evidence can be particularly difficult where scientific or technical evidence is in question. It has long been recognised that the disciplines of law and science are founded in very different principles and thus their interrelation can be strained. Heffernan points out that the two disciplines “are characterised by notable differences in ideology, expectation, methodology, language and discourse.” [402]

2.296          Applying scientific information to principles of law can prove to be difficult task. This is because, according to Heffernan:

“Lawyers and scientists are creatures of their respective cultures; they neither approach litigious issues in the same way nor speak the same professional language. The search for scientific truth is a markedly different enterprise from the law’s inquiry into the proof of allegation and counter-allegation.”[403]

2.297          Problems can arise therefore where a party seeks to present expert evidence about a recent scientific advance or other novel or emerging area of expertise which may not have received widespread approval or recognition.

2.298          It can be difficult for a lay judge or jury, entirely unacquainted with scientific or technical fields of expertise, to assess whether the evidence coming before them has a reliable and well-established foundation, or whether it amounts to what has been termed ‘junk science.’ [404] The term ‘junk science,’ refers to the abuse of science and scientific terminology in the courtroom setting by importing irrelevant or inaccurate evidence to advance a party’s arguments

2.299          The evidence envisaged under this section is that which relates to new and emerging areas of expertise; scientific advances and new theories and techniques that have not been previously tested in the courts. The various jurisdictions have taken different approaches regarding how best to establish the reliability of such expert testimony.

(1)                Ireland

2.300          In Ireland, all that is required in order for a party to have expert evidence adduced is that the party can prove that the expert evidence is relevant in that it is necessary to resolve the issue at hand, and that the party can prove that the person in question is a sufficiently qualified expert in the particular field.

2.301          In contrast with other jurisdictions, there is no admissibility test which requires the party to demonstrate that the expert evidence they purport to adduce can be considered as being founded on a sufficiently reliable basis.

(a)                Problems Generated by Lack of Formal Reliability Test

2.302          It is clear that in certain instances it may not always be clear to the court whether expertise would be helpful in a particular case, or whether or not an issue is outside the scope of expertise of the finder of fact.

2.303          Although the majority of this evidence will undoubtedly be trustworthy and dependable, there have been examples of infamous cases albeit a small number) where inaccurate, for the most part scientific, evidence has led to serious miscarriages of justice.

(b)               Judicial Discretion to Refuse Unreliable Evidence

2.304          It can be argued that the existing admissibility requirements do, to a certain extent, address the issue of reliability, as deciding on the appropriateness of a witness’ expertise and the necessity for the evidence to be based on the facts will inevitably involve a determination of how reliable the evidence is.

2.305          Notwithstanding the absence of a set test, the court at all times retains the discretion as to whether to admit expert evidence or not, and the case law demonstrates that the Irish courts are keenly aware of the potential for unreliable evidence and will not hesitate to reject evidence that does not meet the appropriate threshold.

2.306          Although the cases in this jurisdiction that have considered the trustworthiness of expert evidence, and the related need for a reliability requirement are rare, on a number of occasions expert evidence has been rejected on the basis that it is not sufficiently supported by legitimate expertise.

(c)                Case Law Rejecting Expert Evidence

2.307          A case where expert evidence was rejected as unreliable is The People (DPP) v Fox.[405] Here, the prosecution sought to rely on the evidence of an expert on handwriting to prove that it was the accused’s signature on a document in issue. The Court rejected this evidence, finding that the evidence in question was not backed by any scientific criteria which would have enabled the finder of fact to test the accuracy of the expert’s conclusions.

2.308          It was pointed out that it was common practice when giving expert evidence of handwriting to give the similarities and dissimilarities of the writing which the expert relies on in evidence and this was not done here. Similarly, the expert was criticised for his sole reliance on lower case writing without giving an explanation for doing so.

2.309          Similarly in NC v DPP [406] the Supreme Court refused to prosecute the accused in circumstances where hypnosis had been used on the complainant to recover suppressed memory of sexual offences. It was not that hypnosis was seen as an illegitimate form of expertise that lead to this result but rather the fact that the therapist was not present at the trial for questioning about the procedures involved, and considerable uncertainty surrounded the date and circumstances of the alleged recovery of memory.

2.310          The Court was thus concerned about the absence of an “effective test or control of the mechanism of alleged recovered memory.” This would infer that the Irish courts will require a high level of proof of the reliability of any novel form of expertise, even if no formal reliability test has been enunciated.

(d)               Reliability of DNA Evidence

2.311          The majority of judicial consideration on the appropriate reliability test for expert testimony has been based on an examination of DNA evidence and its trustworthiness.

2.312          In its Consultation Paper on the Establishment of a DNA Database the Commission outlined a number of cases that had considered the reliability of DNA evidence.[407] It was noted that the reliability of DNA technology has been accepted in general terms in Ireland in The People (DPP) v Lawlor[408] and in The People (DPP) v Horgan.[409]

2.313          The Commission also outlined, however, a number of cases where the individual DNA evidence given in the case was criticised or rejected. For example, in People (DPP) v Howe[410] an acquittal was directed as the DNA evidence was considered unreliable for two reasons. First, the forensic scientist had no qualification in statistics therefore could not determine the probability of the DNA belonging to another person. Second, the prosecution had not disproved that the accused did not have a brother, who could have had similar DNA.

2.314          A strong warning was given in the context of DNA testimony in People (DPP) v Allen[411] where the Court of Criminal Appeal admitted the evidence, but stated:

“Expert evidence comparing DNA profiles is a comparatively recent scientific technique, and indeed it would appear that it is still being perfected. As in many scientific advances, the jury have to rely entirely on expert evidence. One of the primary dangers involved in such circumstances is that, the matter being so technical, a jury could jump to the conclusion that the evidence is infallible. That, of course, is not so in the case of DNA evidence, at least in the present state of knowledge.”[412]

(e)                Conclusion

2.315          The case law already discussed demonstrates that even though there is no formal test or yardstick which the court can use to help determine whether or not the expert evidence which a party wishes to adduce is reliable, in reality the Irish courts are anxious to ensure that expert evidence is substantially sound before permitting it to form part of the evidence before the court.

2.316          In contrast with other jurisdictions there has been little judicial debate or commentary in this jurisdiction on the reform of this area or on the merits of the introduction of additional admissibility criteria based on the reliability of the evidence.

2.317          However, there is growing academic literature on the issues of reliability and junk science, and other jurisdictions have implemented various reforms in this context. Legal developments in the United States in this area have been the main catalyst for reform internationally, and notable case law in the US (for example the Frye and Daubert decisions) has been used as the basis for discussion on the need to introduce a reliability test wherever this has been considered.

(2)                United States

2.318          The American courts have imposed more rigorous admissibility requirements than most other common law jurisdictions in an effort to prevent unreliable testimony and to ensure against the proliferation of junk science.

(a)                The Frye Test

2.319          The US debate on this issue began with the landmark decision in Frye v United States.[413] Here, the defendant sought to adduce expert evidence about the results of a systolic blood pressure deception test, the precursor to the lie detector test, to prove his innocence. The court refused to allow the evidence to be admitted. In the course of the judgment they set down a new test for the reliability of expert evidence,

“Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.”[414] (emphasis added)

2.320          This test engendered considerable debate and sometimes criticism in the US but became the dominant test in the US for the next 70 years.[415] It required parties who wished to adduce expert evidence to prove that the evidence in question had gained ‘general acceptance’ in the field of expertise from which it purported to belong, by demonstrating that the principle had gained consensus amongst a considerable body of experts in the field.

(b)               The Daubert Test

2.321          The decision in Daubert v Merrell Dow Pharmaceuticals, Inc[416] was the next major case to fuel the growing debate on ‘junk science.’ This was a civil action where the plaintiffs claimed that a pregnant mother’s use of the defendant’s anti-nausea drug, Bendectin, could result in her child developing limb defects and sought to advance significant expert evidence to support this proposition.

2.322          The US Supreme Court refused to admit the plaintiffs evidence and in doing so, held that the Frye test had been impliedly overruled by Rule 702 of the Federal Rules of Evidence which deals with the use of ‘scientific, technical or other specialised knowledge’ by the courts, as nothing in that test required ‘general acceptance’ as a prerequisite to admissibility.[417] On the basis of Rule 702, the Court then set down a new test;

“To summarize: ‘general acceptance’ is not a necessary precondition to the admissibility of scientific evidence under the Federal Rules of Evidence, but the Rules of Evidence - especially Rule 702 - do assign to the trial judge the task of ensuring that an expert's testimony both rests on a reliable foundation and is relevant to the task at hand. Pertinent evidence based on scientifically valid principles will satisfy those demands.”

2.323          Blackmun J recognised that this new test may cause some difficulties in its application, therefore a non-exhaustive list of factors that would help establish if a science or proposition was sufficiently empirically tested were listed in the course of the judgment.[418] These are summarised by Imwinkelried as including;

i)                   Whether the proposition is testable empirically. For example, if an astrologer's claim cannot be tested in that fashion, it cannot qualify as admissible “scientific knowledge” under Rule 702.

ii)                  Whether the proposition has been tested. The proposition may be testable and plausible; however it is a grave mistake to equate the plausible and the proven. The proposition does not deserve scientific status until it has literally been put to the test.

iii)                 Whether the theory has a “known or potential rate of error”. When the technique has an ascertainable error rate, the jury can more intelligently decide how much weight to ascribe to the expert's testimony.

iv)                Whether the proposition has been subjected to peer review and publication. On the one hand, Justice Blackmun insisted that peer review is “not a sine qua non of admissibility”. A given proposition may be so new, or of such limited interest that it is unrealistic to expect it to have been published. On the other hand, peer review is “a relevant… consideration”. Peer review can be circumstantial evidence that the proposition rests on proper scientific procedure. Publication “increases the likelihood that substantive flaws in methodology will be detected. …”

v)                 Whether there are standards for using the methodology. The more standardised the procedures, the easier it is for other scientists to retest the proposition in question, and therefore the sounder the underlying methodology.

vi)                Whether the methodology is generally accepted. Under Frye, general acceptance is an exclusive test for admissibility. Frye elevated general acceptance to the status of a test. Although the Daubert Court rejected Frye, the Court correctly recognised that, like peer review, general acceptance can be persuasive circumstantial evidence that the methodology is sound. When a methodology is old enough to have garnered general acceptance, other scientists have had a chance to retest the proposition. If the technique still enjoys widespread support, presumably no one has identified significant deficiencies in the research. [419]

2.324          This decision can be seen as moving the focus from requiring the evidence to be generally accepted, to requiring the evidence to be empirically validated. Bernstein argues Daubert requires the court to address two distinct issues:

“First, are the studies or data upon which the expert is relying trustworthy? Second, if so, are these studies or data actually probative of the issues before the court?”[420]

2.325          Blackmun J in Daubert also explained that whereas Frye focused “on exclusively ‘novel’ scientific techniques,’ Daubert was not so limited and any expertise sought to be adduced in evidence, not just new evidence, would have to conform to its requirements.[421]  This greatly expanded the categories of evidence which could be scrutinised in terms of their reliability, as Frye jurisdictions had often treated ‘soft-science’ as being exempt from compliance with the general acceptance test.[422]

(c)                Post-Daubert Position

2.326          In the aftermath of the Frye and Daubert decisions, different approaches were taken by the various states. Although a number of states still subscribe to the Frye test, the majority of states now follow the Daubert standard.[423] Indeed, the case law following Daubert saw the courts become increasingly strict about the reliability of expert testimony.

(i)                 Expert Opinion can be Unreliable even if Methodologies are Sound

2.327          For example in General Electric Co. v Joiner[424] the respondent claimed that his exposure to certain materials used in the course of his employment “promoted” his development of small cell lung cancer and advanced expert evidence in the form of rodent studies and other vague epidemiological data in support of his claim. The petitioners criticised the testimony of the experts in that it was “not supported by epidemiological studies . . . [and was] based exclusively on isolated studies of laboratory animals.”

2.328          The Supreme Court approved the decision of the District Court to find in favour of the respondents, finding that the studies cited by the expert were not sufficient support for his conclusions. For the Court, Rehnquist J urged future courts to exclude expert evidence that relied on misguided reasoning to infer causation from the available evidence, even if the underlying general methodology used was valid:

“…conclusions and methodology are not entirely distinct from one another. Trained experts commonly extrapolate from existing data. But nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence which is connected to existing data only by the ipse dixit of the expert. A court may conclude that there is simply too great an analytical gap between the data and the opinion proffered.”[425]

(ii)               Expert Opinion can be Unreliable Even Where the Expertise is Non-Scientific

2.329          Likewise in Kumho Tyre Co v Carmichael[426] the excluded testimony in question was that of a tyre expert who sought to give evidence of “tyre technology” to the effect that he could give the reasons for tyre failure having examined the tyre in question.

2.330          The Supreme Court expanded on Blackmun’s comments in Daubert to the effect that the range of expert testimony that could be required to prove its methodologies were sound is no longer confined to scientific fields but can be applied to all fields of expertise, even those where expertise is being claimed as a result of technical or practical experience:

“We do not believe that Rule 702 creates a schematism that segregates expertise by type while mapping certain kinds of questions to certain kinds of experts. Life and the legal cases that it generates are too complex to warrant so definitive a match.”[427]

2.331          Breyer J acknowledged that the criteria set down in Daubert which are to be used to assess the validity of any expert testimony are not definitive but are meant to act as helpful guidelines. This is a recognition of the fact that not all types of expert testimony are conducive to scientific methods of empirical testing.

2.332          However, Breyer J did find that some of the Daubert criteria could be used to evaluate the validity of non-scientific evidence, even experience based testimony, and that the individual court in each case should have a certain degree of leeway in relation to what factors are used to determine the reliability of expert evidence. He gave the following examples:

“In certain cases, it will be appropriate for the trial judge to ask, for example, how often an engineering expert’s experience-based methodology has produced erroneous results, or whether such a method is generally accepted in the relevant engineering community. Likewise, it will at times be useful to ask even of a witness whose expertise is based purely on experience, say, a perfume tester able to distinguish among 140 odors at a sniff, whether his preparation is of a kind that others in the field would recognize as acceptable.” [428]

(d)               Conclusion

2.333          The willingness of states to apply increasingly stringent admissibility requirements came about in the wake of an increased awareness that much of the expert evidence that was being proffered in litigation at the time was proving to be erroneous or inaccurate.[429]

2.334          The tests in Frye and Daubert greatly reduced the possibility for inaccurate evidence or junk science being admitted as expert testimony, and both tests have been subject of copious commentary in the US, both academically and in the case law.[430]

(3)                Australia

2.335          In its Issues Paper on Evidence, which formed part of its Review of the Evidence Act 1995, the Australian Law Reform Commission gave detailed consideration to what they term ‘the field of expertise rule,’ or the requirement that “claimed knowledge or expertise should be recognised as credible by others capable of evaluating its theoretical and experiential foundations.”[431]

2.336          The Commission explained that the Uniform Evidence Act does not contain a specific ‘area of expertise’ requirement, and that all the act requires is that the person purporting to give expert evidence have “specialised knowledge.”[432]

2.337          They further explain that the ‘field of expertise’ rule has been the subject of contention at common law and that although different approaches have been taken within the various Australian jurisdictions and courts, that the applicable test has not yet been fully resolved.[433]

(i)                 High Court of Australia

2.338          The High Court of Australia originally adopted a ‘general acceptance’ style test. In HG v The Queen.[434] The court held that in order to qualify as expert evidence, the expert’s knowledge and experience of a particular area must be:

“….sufficiently organised or recognised to be accepted as a reliable body of knowledge or experience.”[435]

2.339          The question of reliability was reconsidered more recently in Velveski v The Queen.[436] Here, the appellant was convicted of the murder of his wife and three children and appealed on the grounds that inter alia expert evidence should not have been admitted from the prosecution which sought to prove that the appellant’s wife had been murdered rather than committed suicide. The appellant argued that such evidence should not be admissible as it was not established that, based on the test in HG v The Queen:[437]

“...there is a reliable body of knowledge and experience, based on the observation of wounds, which would enable a person to express an expert opinion whether particular wounds were self-inflicted.”[438]

2.340          This was rejected on appeal where it was held that whether wounds may have been suicidally self-inflicted is capable of being the subject of expert evidence if a suitable foundation as to the witnesses' training, study or experience has been laid. They went on to discuss what would constitute sufficient ‘training, study or experience:’

“[T]he words used in the section, necessarily include, as they must in all areas of expertise, observations and knowledge of everyday affairs and events, and departures from them. It will frequently be impossible to divorce entirely these observations and that knowledge from the body of purely specialised knowledge upon which an expert's opinion depends. It is the added ingredient of specialised knowledge to the expert's body of general knowledge that equips the expert to give his or her opinion.”[439]

2.341          These comments could be interpreted as a move away from assessing reliability in terms of how well it has been organised or recognised towards a Daubert-style assessment of the evidence in terms of the expert’s training, study or experience.

2.342          These judgments have led commentators to find that the approach of the Australian High Court is that while recognition may be one basis for a conclusion of reliability, under the uniform Evidence Acts the ultimate test is reliability’ of the expert’s knowledge or experience in an area.[440]

(ii)               South Australia

2.343          In the South Australian decision of R v Bonython[441] King CJ set down a test for the admissibility of expert evidence in that jurisdiction. This test has been cited with approval on several occasions in various common law jurisdictions.

“Before admitting the opinion of a witness into evidence as expert testimony, the judge must consider and decide two questions. The first is whether the subject matter of the opinion falls within the class of subjects upon which expert testimony is permissible. This first question may be divided into two parts; a) whether the subject matter of the opinion is such that a person without instruction or experience in the area of knowledge or human experience would be able to form a sound judgment on the matter without the assistance of witnesses possessing special knowledge or experience in the area and b) whether the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organised or recognised to be accepted as a reliable body of knowledge or experience, a special acquaintance with which of the witness would render his opinion of assistance to the court. The second question is whether the witness has acquired by study or experience sufficient knowledge of the subject to render his opinion of value in resolving the issue before the court.”[442]

2.344          Therefore King CJ’s admissibility test can be summarised as requiring:

1.     The evidence comes within the categories of subjects on which expert evidence is admissible. This can be broken down to two further requirements;

a.     the subject matter of the evidence is one that requires special knowledge or assistance in order to make a sound judgment on (i.e. it is outside the scope of knowledge of the ordinary person)

b.    the subject matter has been accepted as forming part of a sufficiently organised or recognise reliable knowledge or experience to be considered a reliable body of knowledge or experience

2.     The expert has sufficient qualifications or experience to be considered an expert in the field.

(iii)              Victoria

2.345          In contrast with South Australia, the Victoria Court of Criminal Appeal rejected the general acceptance rule in R v Johnson.[443] Here Brooking J stated the applicable admissibility requirements in that jurisdiction:

“Provided the judge is satisfied that there is a field of expert knowledge … it is no objection to the reception of the evidence of an expert within that field that the views which he puts forward do not command general acceptance by other experts in the field.” [444]

(iv)              Reform of the Australian Admissibility Requirements – The Addition of a Reliability Test

2.346          The need to have some sort of reliability test on the types of knowledge submitted to be the subject matter of expert evidence was recently discussed by the Australian, the New South Wales, and the Victorian Law Reform Commissions as part of their combined review of Uniform Evidence Law in 2005. [445]

2.347          The Commissions acknowledged the ongoing debate as to whether an additional admissibility requirement relating to reliability of the evidence should be introduced and summarised the different approaches that have been adopted by the various Australian courts and jurisdictions.[446]

2.348          The Commissions referred to the Frye and Daubert tests and acknowledged that it has not yet been resolved to what extent these should be apply in the context of the Uniform Evidence Act. In the Issues paper the Commission summarised the arguments in this regard:

“One view is that the ‘specialised knowledge’ requirement of section 79 should be interpreted as imposing a standard of evidentiary reliability, so that expert opinion evidence must be derived from a reliable body of knowledge and experience. At the least, aspects of the field of expertise test, including ‘general acceptance’ and Daubert-style reliability criteria may be able to be used to help determine the probative value of evidence in the exercise of the general discretion to exclude evidence. On the other hand, there may be concern about the restoration of a field of expertise rule, contrary to legislative intent, through such interpretations of section 79.”[447]

2.349          In the final report, the Commission expressed the view that it was unnecessary to recommend an amendment to import any of the tests, such as the Frye test, that have been considered necessary at common law, or to clarify any aspects of the ‘specialised knowledge’ requirement of s 79. Therefore, the Commissions appeared satisfied to let determination of reliability to be decided by the court on a case by case basis without any additional admissibility barriers such as requiring the evidence to have been generally accepted (Frye) or requiring the underlying methodology to be scientifically verifiable (Daubert).

(4)                England & Wales

2.350          As in this jurisdiction, there is no formal or statutory reliability test for admissibility of expert evidence. Expert evidence will be admitted once it is relevant and the person seeking to give the evidence is sufficiently qualified to be considered an expert.

2.351          Relevancy hinges on the ability of the evidence to be of assistance in helping the court to reach a ‘fully informed decision,’[448] a question that will in turn hinge on whether the issue is one which an ordinary person would require instructions on the essentials of the necessary field of expertise to make this fully informed decision.[449]

(a)                Judicial Discretion and Flexible Case by Case Approach

2.352          Rather than create set categories of permitted evidence, or a formal reliability test for admissibility, the English courts have taken a case by case approach in assessing new scientific developments that come before the courts.[450]

2.353          This was acknowledged by Gage LJ in R v Harris & Ors[451] where he stated:

“There is no single test which can provide a threshold for admissibility in all cases. As Clarke demonstrates developments in scientific thinking and techniques should not be kept from the Court. Further, in our judgment, developments in scientific thinking should not be kept from the Court, simply because they remain at the stage of a hypothesis. Obviously, it is of the first importance that the true status of the expert's evidence is frankly indicated to the court.”[452]

2.354          In recent years, the English courts have had to decide on the reliability of certain types of new and novel types of scientific and technical evidence in a number of cases. However, the court has resisted the formulation of an additional admissibility test in the form of a reliability test.

(b)               Focus on the Qualifications of the Expert

2.355          In R v Robb,[453] the prosecution sought to adduce an expert in phonetics to give expert voice identification evidence after repeatedly listening to recordings of the defendant’s voice.

2.356          Bingham L.J. laid down a two-pronged test for admissibility of expert evidence; first, whether study and experience will give a witness’s opinion an authority which the opinion of one not so qualified will lack, and if so, second, whether the witness in question is peritus, that is skilled,[454] and has adequate knowledge. Bingham LJ continued:

“If these conditions are met the evidence of the witness is in law admissible, although the weight to be attached to his opinion must of course be assessed by the tribunal of fact.”

2.357          The test propounded here by Bingham LJ arguably failed to take into account the reliability of the evidence at all, focusing instead on expert giving the evidence and their qualifications.

2.358          In R v Stockwell[455] a facial mapping expert was called by the prosecution to help prove that the defendants’ disguised face appeared on video films taken during a bank robbery and attempted robbery. On appeal, the Court had to decide if this evidence was rightly admitted.

2.359          The English Court of Appeal observed that the trial judge had described facial mapping evidence as ‘breaking new ground’  went on to approve his view that “one should not set one’s face against fresh developments, provided that they have a proper foundation,” therefore allowing the evidence to be admitted.

2.360          In relation to the test for admissibility, the court appeared to affirm the approach taken in Robb:

“In such circumstances we can see no reason why expert evidence, if it can provide the jury with information and assistance they would otherwise lack, should not be given. In each case it must be for the judge to decide whether the issue is one on which the jury could be assisted by expert evidence, and whether the expert tendered has the expertise to provide such evidence.”[456]

(c)                Move towards a Reliability Test?

2.361          The decision in R v Gilfoyle[457] came closer to referring to reliability as being requisite for admissibility. Here, the court refused to admit evidence of a psychologist, submitted by the defence, to prove that the deceased was in such a frame of mind prior to death that she was likely to commit suicide. The court held that this ‘psychological autopsy’ was a new developing brand of science that had not yet been properly accepted within its field of expertise.

2.362          Rose L.J. observed that expert evidence “based on a developing new brand of science or medicine” would not be admissible “until it is accepted by the scientific community as being able to provide accurate and reliable opinion.”[458] The court cited Strudwick & Merry[459] and Frye[460] in support of this view.[461]

(d)               Return to Traditional Qualifications-Based Approach

2.363          However, Gilfoyle was criticised in R v Dallagher[462] where Robb was again reasserted. In this case, the defendant successfully appealed his murder conviction on the basis that fresh evidence had emerged in the form of misgivings about the extent to which ear print evidence alone could safely be used to identify a suspect.

2.364          The court here pointed out that the American approach in Frye[463] had now been overtaken by the test propounded in Daubert[464] and cited Cross & Tapper as encapsulating the current test in England:

“The better, and now more widely accepted, view is that so long as the field is sufficiently well-established to pass the ordinary tests of relevance and reliability, then no enhanced test of admissibility should be applied, but the weight of the evidence should be established by the same adversarial forensic techniques applicable elsewhere.”[465]

2.365          Although the court here mentioned the Daubert test, as well as US Federal Court Rule 702 on which that decision was based, the Court of Appeal failed to elaborate whether Daubert criteria should be applied in England to ensure that the evidence had a sufficiently certain grounding, but seemed to infer that the decision about the reliability and relevancy of the evidence should continue to be decided by the judge on a case by case basis.

(e)                Problems with Lack of Reliability Test

2.366          Although the court in Dallagher[466] refused to find that the evidence should have been ruled inadmissible on the basis of the Robb test, at the retrial this evidence was not re-introduced by the prosecution and ultimately the accused’s conviction was quashed. This highlights the potential for inaccurate evidence to lead to false convictions.

2.367          Another example of this is R v Cannings[467] where the appellant appealed her murder conviction on the basis of new advances in scientific understanding of sudden infant death syndrome which showed that multiple cases of the syndrome in one family was not so rare as had been stated at trial by an expert witness. Again, the appellant had spent time in prison before these developments came to life, underlining the potential for untested evidence to have onerous implications for accused persons.

(f)                 Confusion in Recent Case Law

2.368          More recently, in R v Luttrell[468] the appellants sought to argue that a requirement for admissibility includes proving that the evidence can be seen to be reliable because the methods used can be sufficiently explained in cross examination to test veracity or falsehood. This was rejected by the court, Rose L.J. stating:

“We cannot accept that this is a requirement of admissibility. In established fields of science, the court may take the view that expert evidence would fall beyond the recognised limits of the field or that methods are too unconventional to be regarded as subject to the scientific discipline. But a skill or expertise can be recognised and respected, and thus satisfy the conditions for admissible expert evidence, although the discipline is not susceptible to this sort of scientific discipline.”[469]

2.369          In the course of this judgment Rose LJ acknowledged that two conditions for admissibility have been recognised; first, that study or experience will give a witness's opinion an authority which the opinion of one not so qualified will lack; and secondly the witness must be so qualified to express the opinion. Confusingly, Rose L.J. found the basis for this two-pronged requirement not only in Robb but also in the South Australian decision R v Bonython.[470]

2.370          However, in reality the decision in R v Bonython[471] imposes more stringent requirements than Robb as it contains the added requirement, not present in Robb, that “the subject matter of the opinion forms part of a body of knowledge or experience which is sufficiently organised or recognised to be accepted as a reliable body of knowledge or experience.”[472]

2.371          It is apparent from this that Rose L.J. considered reliability relevant to deciding if the conditions for admissibility are met, but he was of the view that in itself reliability goes to its weight. Furthermore, he did not seem to be of the view that the reliability requirement went so far as the necessitate proof that the methods used can be tested in cross examination, but merely requiring proof that the evidence had been sufficiently organised or recognised as being so. 

2.372          Similar confusion can be seen in the civil context. For example in Barings plc v Cooper & Lybrand (No.1)[473] Evan-Lombe LJ considered in some detail what the appropriate test for admissibility of expert evidence should be for civil proceedings and found that the test enunciated in R v Bonython[474]constituted a good description of what was necessary to qualify.[475]

2.373          Evans Lombe summarised the principles set out in the governing authorities as requiring the evidence to be based on “recognised expertise governed by recognised standards and rules of conduct” which could clearly be interpreted as requiring the evidence to

2.374          Therefore, despite repeated judicial emphasis that no additional admissibility requirements exist other than those set out in Robb by Bingham LJ, it can be argued that more recent English cases, both civil and criminal, have applied a ‘general acceptance’ test without acknowledging that this test was founded in Frye, which decision was expressly rejected in R v Dallagher.[476]

(g)               Conclusion

2.375          As can be seen, the flexible approach of the English court has made it easier to embrace emerging areas of expertise, and, as can be seen, the courts have shown a willingness to accept many originally unconventional types of identification evidence such as voice identification evidence,[477] facial mapping evidence,[478] ear print evidence,[479] and genetic printing by DNA analysis.[480]

2.376          Furthermore, the English courts have repeatedly emphasised that the appropriate test for admissibility is one that asks first, whether study or experience will give the opinion of a witness an authority lacking in the opinion of one not so qualified, and second, whether the person is sufficiently qualified.

2.377          However, the negative consequences that can result from allowing misleading theories or ‘junk science’ to advance a party’s case are also evident from the above mentioned cases.

2.378          As a result, the courts should be wary that any desire to embrace new scientific developments does not lead to the introduction of unreliable and inaccurate evidence capable of leading to unsafe convictions.

2.379          Hodgkinson and James are critical of the lack of judicial debate about how best to deal with expert evidence and the lessons that can be learned from other jurisdictions.[481] They recommend that the English courts would do well to consider applying the test in R v Bonython[482]or at the very least, introducing some a sort of Daubert style judicial guidance to help the court assess whether the evidence is reliable to go before the court.

(5)                A Reliability Test for Ireland?

2.380          The question to be asked is whether imposing a Daubert-like test for admissibility in Ireland would be workable or beneficial? Imwinkelried argues that in the light of the proliferation in use of expert witnesses in all types of litigation in Ireland, and the substantial threat to justice posed by flaws in expert testimony, the Irish courts would do well to take heed of US developments in this area, and insist that any evidence adduced be empirically tested and supported.[483]

2.381          This part of the chapter will now summarise the arguments that have been made for and against the introduction of a reliability test.

(a)                Disadvantages – Reasons to Retain the Status Quo

·           It has been argued that there would be a certain degree of circularity in asking a court to decide on the reliability of evidence that is essentially being introduced due to the fact that it outside of the range of knowledge of the court.[484]

·           It has also been suggested that the reason for the lack of judicial scrutiny on the need for a reliability requirement can be explained by the fact that our system is adversarial in nature and therefore as a result, the process itself tends to weed out unreliable testimony through cross-examination from the other party thus negating the need for such a requirement at admissibility stage.[485]

·           It has often been contended then that reliability is more appropriately an issue to be taken into account when assessing the weight of the evidence rather than admissibility.[486] In the context of jury trials assessing the admissibility of evidence after it has been heard could prove difficult for lay jurors.

·           Heffernan points out that there are a number of differences in the Irish and American legal systems that might have a bearing on this issue.[487] She notes in particular that juries play a much bigger role in American litigation than in this jurisdiction. The risk of juries being unduly swayed by effusive and ostentatious expert witnesses has long since been recognised as being far higher than the risk of influencing a judge well versed in such routines. Similarly, there are a number of procedural differences between the Irish and American systems. For example the summary judgment mechanism in the US aims to resolve proceedings at a pre-trial stage, or at least, reduce the contentious issues at trial, and it is here that admissibility issues are often resolved. Ireland has no equivalent procedure, which means that the Irish system might be far less procedurally conducive to applying and enforcing a Daubert based test, if introduced.

·           It can also be argued that a ‘general acceptance’ test, or a ‘reputable body of opinion’ test of reliability, would in reality be too strict and too conservative, and would cause much useful and reliable evidence to be excluded. It could result in courts lagging behind advances in science and other learning.[488]

·           Finally, it can be argued that the introduction of a reliability test is unnecessary and superfluous. Despite high profile examples of miscarriages of justice caused by unreliable or inaccurate expert testimony, such cases are rare and the large majority of expert testimony that comes before the court will relate to well established and undoubtedly reliable principles of expertise. Furthermore, as pointed out by Hodgkinson and James:

“….most of the well publicised miscarriages of justice arise not from the use of novel but flawed science but from the incorrect application of well established scientific principles and techniques[489] or from a misunderstanding of sound science[490] or a failure of the prosecution to disclose material that could undermine its scientific case[491] and/or, occasionally, deliberate misrepresentations of the effect of forensic work.[492][493]

(b)               Advantages – Reasons to Introduce a Reliability Test

·           It is equally arguable that Ireland would benefit from introducing a reliability threshold for the admissibility of expert evidence, similar to that introduced in other jurisdictions such as the US.

·           For instance, as discussed below, a reliability requirement would go a long way towards eliminating the presence of junk science from being submitted as evidence.[494]

·           Hodgkinson & James argue that the failure to encompass a reliability requirement could have unfortunate consequences for example where ‘pseudo-science’ or new scientific developments are being proffered as evidence as there is no onus on the expert to show that there is a link between the issues in the case and the reliability of the expert knowledge.[495]

·           It has already been noted that the degree and range of subject matter of specialisation has escalated over the years with new and more specialised forms of ‘expertise’ appearing with more and more regularity. It can be difficult to expect a court unacquainted with the complex evidence with which they are presented, to evaluate the merits of this evidence or its reliability.

·           Requiring juries to evaluate the appropriate weight to accord to new and untested scientific advances has the potential to lead to miscarriages of justice, and that the better approach would be to prohibit expert evidence in avant-garde areas of science or technology from being admitted until the area has been sufficiently accepted or recognised as a reliable body of knowledge.[496]

2.382          Based on the foregoing, the Commission has provisionally come to the conclusion that the arguments in favour of a reliability test are greater and that it should be introduced as an additional requirement for admissibility of all expert testimony.

2.383          The Commission provisionally recommends that a reliability test should be introduced as an additional requirement for admissibility of all expert testimony.

(c)                Appropriate Form of Reliability Test

2.384          The introduction of a reliability test has been considered to have considerable merits. However, the question remains as to what form such a test should take and how should it be introduced into Irish law.

(i)                 Statutory Provision

2.385          One option that could be taken is the formulation of an express formal and binding test for admissibility the elements of which would have to be satisfied by all parties seeking to adduce expert evidence.

2.386          However, it is clear that there may be difficulties with creating such a test in a stand-alone provision for reliability of expert evidence, and it would be more appropriate to incorporate a reliability test provision into a larger instrument on expert evidence in general containing all applicable rules relating to expert evidence, such as part of an Evidence Code or Act.

2.387          Furthermore, the approach taken in other jurisdictions, even those where an Act of Code of Evidence is provided for, generally appears to be that the statutory provisions contain general provisions giving the judge in an individual case the discretion to determine whether or not to admit the evidence, and the appropriate test to be applied by the judge in coming to this decision tends to be formulated in the case law.

(ii)               Judicial Guidelines

2.388          A more appropriate approach, it is submitted, is to create a judicial guidance note on admissibility which outlines the appropriate test that should be applied by the trial judge when confronted with novel or other areas of expertise the reliability of which is not clear.

2.389          This could be applied as a non-exhaustive and non-binding guide that can be adverted to by the trial judge in assessing whether or not to admit expert evidence.

2.390          The Commission provisionally recommends the introduction of a judicial guidance note outlining the factors that can be taken into account by the trial judge when assessing whether the expert evidence in question meets the requisite reliability threshold.

(d)               Requisite Contents and Elements of a Test

2.391          Once the appropriate form has been decided on, the appropriate wording and elements of the test to be introduced must be considered. From the above discussion, two discernible approaches appear to have been taken in different jurisdictions.

(i)                 General Acceptance Test

2.392          The approach originally taken in the US in Frye, which also constitutes the test applied in Bonython,[497] is to require the evidence to have reached a set level of acceptance within the field of expertise to which it relates which can then be used to vouch for its validity.

2.393          This requires the party wishing to adduce expert evidence to demonstrate that the principle has gained consensus, acceptance and recognition among a considerable body of experts in the field.

(I)                 Advantages

·           This test is advantageous as it is clear that the body best placed to assess the merits and reliability of the evidence is the expert community from which the principle stems. If the evidence has achieved acceptance within the expert field itself, its reliability is greatly bolstered. This helps to ensure that the trial judge will not struggle with the task of understanding and assessing the reliability of evidence entirely outside of the scope of his or her knowledge.

·           This argument is strengthened by the fact that a similar approach is taken in professional negligence cases where the question of negligence is based on whether or not the action taken is one which no reasonable professional in the area would have taken.  

·           It can be argued that the general acceptance test does not impose too onerous a criterion where the expertise is sufficiently sound in terms of reliability. Such evidence is likely to have achieved general acceptance without difficulty. Evidence that has not been recognised by a large body of experts within the field is more likely to be considered unreliable even where other factors are used to determine this.  

·           The general acceptance requirement would also ensure that there would be a considerable body of experts who recognise the theory and would thus form a considerable body of experts available to give evidence on the issue. It could thus promote consistency in decision making.[498]

(II)                Disadvantages

·           It can be argued however that permitting the evidence to be adduced solely on the basis of its acceptance by the expert community from which it stems removes the decision about its reliability away from the court and into the hands of the expert community, which may be seen as a usurpation of the role of the judge and jury.

·           Furthermore, the general acceptance test, which requires acceptance amongst a considerable body of experts, imposes a much higher burden on the expert than does the test for professional negligence, which assesses negligence on the basis of action that no reasonable professional would have taken.

·           It can be argued that satisfying the general acceptance standard will not automatically ensure the reliability of evidence. Peer review is a clear example that a theory has achieved recognition and acceptance within a particular field of expertise, yet assessment in terms of peer review has been repeatedly criticised.[499] McMullan gives the example of the Sokal article incident where an article was published in an American peer reviewed article and its author later admitted the theory discussed in the article to be a hoax.[500]  Its acceptance in the journal highlights the potential inadequacy of peer reviewing as a filtering mechanism for unreliable areas of expertise. 

·           The test can also be criticised in that it precludes certain evidence from the outset, namely evidence that is so novel and new that it has not yet been assessed by the expert community to which it relates, without assessing the foundational basis of the evidence at all.

·           It may occur that a case arises where the key point of expertise is so novel and technical that it has not been considered before. This fact should not be used to exclude such evidence when in reality it could have an important bearing on the facts in issue.

·           There may also be difficulties in determining the appropriate level of ‘general acceptance’ and what constitutes a considerable body of expert recognition for the purpose of the test.

·           It has also been argued that this test tends to prohibit the admission of new research undertaken specifically for the purposes of litigation which can lead to novel but reliable evidence being excluded.[501]

·           An automatic prohibition on evidence not meeting the appropriate standards in terms of reputation, as opposed to substance, is not desirable.

2.394          The Commission provisionally recommends that the general acceptance test, by focusing on the number of experts in the area that recognise the theory, rather than assessing the subjective merits of the theory itself, imposes too onerous a burden in terms of its provenance as opposed to its content to be considered an appropriate test to determine the reliability of the evidence.

(ii)               Empirical Validation

2.395          An alternative test which could be imposed is one similar to that propounded in Daubert, namely a test that focuses on the evidence itself in terms of its underlying methodologies and results to examine its reliability. Such a test should take the form of a non-exhaustive range of factors that would be taken into account by the court when assessing the evidence, general acceptance being just one of these factors.

2.396          The decision in Daubert provided useful guidance as it gave examples of those factors that can be used to determine reliability. Based on this decision, and on other guidelines[502] that have been suggested in relation to this, the principal factors that should form the basis of any reliability test based on empirical validation include;

1.     Are the principles behind the theory consistent in that its proponents are in agreement about its constituent elements which would enable it to be empirically testable and falsifiable?

2.     Have the principles and procedures behind the theory been empirically tested in that it can be demonstrated by evidence of actual experiences rather than hypothetical situation?

3.     Are the conclusions reached by the expert backed up by sufficient supporting evidence and logical based on the principles underlining the theory?

4.     Has the theory a known or potential rate of error?

5.     Has the theory been subjected to peer review and publication?