Gauging the reliability of scientific evidence in tort

AuthorLiz Heffernan
PositionLecturer in Law, University College Dublin
Judicial Studies Institute Journal [6:1
The objective of this paper is to explore the role of science
in the resolution of proceedings in tort. Scientific evidence,
broadly defined, encompasses just some of the many species of
expert evidence that have become a virtual mainstay of tort
litigation in contemporary practice.1 As early as 1960, Mr. Justice
Lavery made the following prescient observation.
This is the age of experts qualified to give opinions
in every field of human knowledge – whether
science, medical or other, in accountancy, finance,
handwriting and technical matters in every aspect
of manufacturing process and so on. I would
certainly not wish to minimise the value of such
evidence, but a sense of proportion should not be
lost. There are innumerable incidents of everyday
life upon which the ordinary person can express a
useful opinion and one which ought to be
Lecturer in Law, University College Dublin. The research for this article was
funded by the Irish Research Council for the Humanities and Social Sciences.
The article has its origins in a paper delivered at the First Annual Society of
Legal Scholars Ireland Conference, Trinity College Dublin, on the 18th
February 2006. My thanks go to William Binchy for the benefit of his insight
on the subject. All opinions expressed and any errors or omissions are my own.
1 See generally Fennell, The Law of Evidence in Ireland, (2nd ed.), (LexisNexis,
Dublin, 2003) ch.6; Healy, Irish Laws of Evidence (Thomson Round Hall,
Dublin, 2004), ch.12; McGrath, Evidence (Thomson Round Hall, Dublin,
2005) ch.6. on the Irish law of expert evidence. See also Kelleher, “Expert
Evidence in Ireland,” (1996) 14 Irish Law Times 42; O’Flaherty, “The Expert
Witness and the Courts,” (1997) 3 Medico-Legal Journal of Ireland 3.
2A.G. (Ruddy) v. Kenny (1960) 94 I.L.T.R. 185 at 189.
2006] Gauging the Reliability of Expert Witnesses 141
The particular incident of everyday life which the learned
justice had in mind was drunkenness which, he concluded, was a
subject on which an ordinary person is qualified to express an
opinion notwithstanding that a garda officer or a medical expert
might be specially qualified to do so.3 Some 45 years later, the
ubiquity of the expert witness has doubtless far outstripped the
expectations of Lavery J. and we are arguably no closer to finding
the sense of proportion in relation to expert evidence of which he
spoke. Certainly, the learned justice could not have foreseen the
level and pace of scientific and technological advancement that
has taken place in our society in the intervening decades. The
consequential application of this burgeoning knowledge in the
courtroom has contributed to the rising profile of the expert
witness. But because matters of science are almost by definition
outside the “innumerable incidents of everyday life upon which
the ordinary person can express a useful opinion,”4 scientific
evidence rarely implicates the overriding concern of the courts,
identified by Lavery J., namely whether there is a need for expert
opinion in a given case.5
The use of science in the trial process does raise other
concerns, however, and chief among them is its reliability as a
form of evidence. The issue has generated surprisingly little
discourse in our case law and jurisprudence and such discussion
as exists tends to be cautious and indirect. In tort actions, the
reliability of expert evidence surfaces, if at all, under the rubric of
the weight of the evidence. Conflicts among expert witnesses are
anticipated and the law leaves it up to the finder of fact, almost
invariably a judge, to decide which expert opinion he should
follow, if at all. Provided that the evidence on which the judge
relies is credible, his ruling will generally be upheld on appeal.
This state of affairs prompted Professor Edward J. Imwinkelried,
a leading authority on the law of evidence, to propose that the
3 See the dissenting judgment of Kingsmill Moore J. in A.G. (Ruddy) v. Kenny
(1960) 94 I.L.T.R. 185 at 189 et seq. for an alternative view.
5Davie v. Edinburgh Magistrates [1953] S.C. 34; A.G. (Ruddy) v. Kenny
(1960) 94 I.L.T.R. 185. The courts are less willing to recognise a need for
expertise from the so-called “soft sciences” such as mental health. See, e.g., R
v. Turner [1975] Q.B. 834; People (D.P.P.) v. Kehoe [1992] I.L.R.M. 481.

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