Gauging the reliability of scientific evidence in tort

• Author: Liz Heffernan
• Position: Lecturer in Law, University College Dublin
• Pages: 140-170

Judicial Studies Institute Journal [6:1

140

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GAUGING THE RELIABILITY OF

SCIENTIFIC EVIDENCE IN TORT

LIZ HEFFERNAN

I. INTRODUCTION

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

admitted.2

 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

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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.

4 (1960) 94 I.L.T.R. 185 at 189.

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.