The Reliability of Expert Evidence: Reflections on the Law Commission's Proposals for Reform
| Author | Liz Heffernan,Mark Coen |
| Date | 01 December 2009 |
| DOI | 10.1350/jcla.2009.73.6.603 |
| Published date | 01 December 2009 |
| Subject Matter | Article |
The Reliability of Expert
Evidence: Reflections on the Law
Commission’s Proposals for
Reform
Liz Heffernan* and Mark Coen†
Abstract The problems associated with the use of expert evidence by the
criminal courts have been the subject of ongoing controversy. The Law
Commission of England and Wales has recently added its voice to the
debate with the publication of a Consultation Paper on the admissibility of
expert evidence. This article examines the current law governing the
reliability of expert evidence. It analyses the Law Commission’s recom-
mendation for the creation of a new statutory rule which would require
the trial judge to assess evidentiary reliability as a matter of admissibility.
The authors chart the emergence of the US Daubert test, on which the
recommendation is based, and consider the lessons to be learned from
American experience. While welcoming the recommendation in prin-
ciple, the authors argue that the crafting and implementation of the
proposed admissibility requirement would present formidable
challenges.
Keywords Expert evidence; Admissibility; Scientific validation;
Miscarriage of justice; Law reform
In recent years, courts have grown increasingly dependent upon scient-
ific methods of proving or refuting allegations of criminal misconduct, a
development which has generated celebration and controversy seem-
ingly in equal measure. Scientific evidence is popularly perceived to be
more reliable than conventional forms of evidence and has been hailed
as a bulwark against traditional causes of miscarriage of justice such as
fabricated testimony and coerced confessions. Paradoxically, scientific
evidence has not escaped its own association with wrongful convictions,
notably in high-profile cases such as the Guildford Four,1Sally Clark2and
Barry George.3How much of the blame for miscarriage of justice should
be laid at the door of expert evidence, as opposed to other aspects of the
process, remains hotly contested. Assuming for a moment that expert
evidence played an ignominious part in the forensic relationship be-
tween law and science, these aberrant cases may represent isolated
* Lecturer and Fellow, Trinity College Dublin.
† LLB (Dublin), BCL (Oxon), PhD candidate, Trinity College Dublin.
1Rv Maguire (1992) 94 Cr App R 133, [1992] 2 QB 926. See also Rv McIlkenny
(1992) Cr App R 287, [1992] 2 All ER 417; Rv Ward [1993] 1 WLR 619, (1993) 96
Cr App R 1. See generally R. Nobles and D. Schiff, Understanding Miscarriages of
Justice: Law, the Media and the Inevitablity of Crisis (Oxford University Press: Oxford,
2000) 198; M. Redmayne, ‘Expert Evidence and Scientific Disagreement’ (1997) 30
UC Davis L Rev 1027.
2 [2003] EWCA Crim 1020. See also Rv Cannings [2004] 1 WLR 2607.
3Rv George (No. 2) [2007] EWCA Crim 2722.
488 The Journal of Criminal Law (2009) 73 JCL 488–507
doi:10.1350/jcla.2009.73.6.603
ruptures rather than a systematic irretrievable breakdown.4Neverthe-
less, the gathering, analysis and presentation of scientific evidence are
complex, subjective processes which hold at least the potential for error
and misunderstanding on the part of the various actors in the trial
process. This practical reality in itself suggests the need for the courts to
enter the zone of scientific evidence with caution.
Ironically, in England and Wales, the traditional judicial attitude to
the admissibility of expert evidence had been distinctly laissez-faire.
Reliability tends to be inferred from the relatively basic showing by the
proponent of the evidence that the witness is a qualified expert.5Occa-
sionally, a trial judge considers scientific validity at the admissibility
stage but without the benefit of any settled framework for such an
inquiry. Beyond this, whether the evidence is trustworthy is a matter for
the jury’s assessment of the weight of the evidence. Several undesirable
consequences may follow. In an extreme case, a jury may be misled into
basing a decision to convict or acquit on an unsound scientific premise.
Even in a typical case, the jury’s function will be complicated by the
need to assess the expert’s working hypothesis (along with the cogency
of the expert’s conclusions and his or her overall credibility). Where the
expertise at issue is particularly difficult to fathom (for example, where
the proceedings centre on a scientific technique that is cutting edge or
keenly disputed among scientists) the jury may simply defer to the
expert. In the heat of the adversarial battle, the jury may prefer one
expert over another based on persona and form rather than the sub-
stance of the testimony.6Broader institutional perils include incon-
sistency in the practice of judges and juries and a corresponding
unpredictability in the outcome of proceedings.
These and related considerations have prompted the Law Commis-
sion of England and Wales to recommend an overhaul of the law
relating to the admissibility of expert evidence. In a Consultation Paper,
the Law Commission provisionally recommends the introduction of
judicial assessment of the reliability of expert evidence as a precondition
to its admissibility.7This recommendation draws heavily on law and
practice in the USA and, specifically, the approach fashioned by the
4 J. Fraser, ‘Science in the Criminal Justice System’, Paper delivered at the Annual
Conference of the Socio-Legal Studies Association, Stirling, Scotland, 29 March
2006.
5 On the admissibility of expert evidence, see generally T. Hodgkinson and M. James,
Expert Evidence: Law and Practice, 2nd edn (Sweet & Maxwell: London, 2007) ch. 3;
M. Redmayne, Expert Evidence and Criminal Justice (Oxford University Press: Oxford,
2001) ch. 5; P. Roberts and A. Zuckerman, Criminal Evidence (Oxford University
Press: Oxford, 2004) ch. 7.
6 See e.g. C. J. Newton, D. J. Terry and R. J. Schuller, ‘Jurors’ Responses to Expert
Witness Testimony: The Effects of Gender Stereotypes’ (2004) 7(2) Group Processes
and Intergroup Relations 131.
7 Law Commission, The Admissibility of Expert Evidence in Criminal Proceedings in
England and Wales: A New Approach to the Determination of Evidentiary Reliability,
Consultation Paper No. 190 (April 2009). The Law Reform Commission of Ireland
published a similar recommendation in 2008. Law Reform Commission, Consultation
Paper on Expert Evidence (LRC CP 52-2008) (December 2008).
The Reliability of Expert Evidence
489
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