Mack’s Expert Evidence Compendium

Dallas Mack | Louise Tansey

Index

Preamble 

Witnesses are generally not permitted to offer opinion evidence; their evidence is normally restricted to testifying about what they saw, did and said or, in some cases, what they heard. Limits on the admissibility of expert opinion evidence reflect the fact that while such evidence can be a “key element in the search for the truth . . . it may also pose special dangers”: White at para. 1.

In general, where a party seeks to elicit “opinion” evidence they must satisfy the two steps for admissibility: White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 CarswellNS 313 (S.C.C.) at paras. 23-24 [White]. First, the evidence must be: (i) relevant; (ii) necessary; (iii) not subject to any exclusionary rule; and (iv) the expert must be “properly qualified”: R. v. Mohan, 1994 CarswellOnt 66 (S.C.C.); R. v. Sekhon, 2014 CarswellBC 379 (S.C.C.) at para. 43. In addition, “in the case of an opinion based on novel or contested science or science used for a novel purpose, the reliability of the underlying science for that purpose”: White at para. 23; R. c. J. (J.), 2000 CarswellQue 2310 (S.C.C.) at paras. 33, 35-36 and 47.

Relevance refers to logical relevance: White at para. 23. Necessity exists to “ensure that the dangers associated with expert evidence are not lightly tolerated” and that “[m]ere relevance or ‘helpfulness’ is not enough: R. v. D. (D.), 2000 CarswellOnt 3255 (S.C.C.) at para. 46. Where the opinion evidence bears upon the ultimate issue an increased scrutiny of relevance and necessity is warranted: R. v. Solleveld, 2014 CarswellOnt 6644 (Ont. C.A.) at paras. 16-20; R. v. Bryan, 2003 CarswellOnt 2068 (Ont. C.A.) at paras. 16-17; R. v. Burns, 1994 CarswellBC 1237 (S.C.C.) at para. 25; R. v. Sekhon, 2014 CarswellBC 379 (S.C.C.) at paras. 75-76. With respect to a properly qualified expert, the expert must, inter alia, be fair, objective and non-partisan (although the evidentiary threshold to establish this is modest): White at paras. 46-51.

Second, the probative value of the evidence must not be outweighed by the prejudicial effect: White at para. 19; J. (J.-L.) at para. 28.

There are exceptions to this general rule. In some situations, witnesses are permitted to provide a “lay opinion”; an opinion about whether a person is impaired by alcohol or a drug is an example: R. v. Graat, 1982 CarswellOnt 101 (S.C.C.); R. v. Bingley, 2014 CarswellOnt 6888 (Ont. S.C.J.), affirmed 2015 CarswellOnt 8987 (Ont. C.A.), affirmed 2017 CarswellOnt 2406, 2017 CarswellOnt 2407 (S.C.C.). In other situations there are legislative schemes which may provide a statutory basis upon which one or more of the Mohan criteria are satisfied: see for example R. v. Bingley, 2017 CarswellOnt 2406 (S.C.C.).

Where it is the defence that seeks to tender opinion evidence the court will generally apply a slightly less stringent standard for admissibility: R. v. M. (B.), 1998 CarswellOnt 4243 (Ont. C.A.) at para. 88; R. v. Bell, 1997 CarswellNWT 4 (N.W.T. C.A.) at para. 28; R. v. Millington, 2015 CarswellBC 2309 (B.C. S.C.) at paras. 21-22.

Where expert evidence is admitted, it is an error for the court to assess that evidence with reference to information, materials or research that is not before the court: R. v. Bornyk, 2015 CarswellBC 126 (B.C. C.A.); R. v. Bahamonde, 2016 CarswellBC 3605 (B.C. C.A.) at para. 24.

Not all expert or scientific evidence is “opinion” evidence however. Evidence which might require scientific knowledge or expertise, does not, in and of itself, make it an opinion. Testimony about accepted scientific facts is not considered opinion evidence and is presumptively admissible: see generally R. v. Hamilton, 2011 CarswellOnt 3491 (Ont. C.A.), leave to appeal refused 2012 CarswellOnt 10888, 2012 CarswellOnt 10889 (S.C.C.), leave to appeal refused 2012 CarswellOnt 10890, 2012 CarswellOnt 10891 (S.C.C.), leave to appeal refused 2012 CarswellOnt 10920, 2012 CarswellOnt 10921 (S.C.C.), leave to appeal refused 2012 CarswellOnt 10892, 2012 CarswellOnt 10893 (S.C.C.); R. v. Paszczenko, 2010 CarswellOnt 6968 (Ont. C.A.).

With these principles that govern admissibility in mind, this compendium reviews areas of expert opinion evidence that have been advanced and the parameters and probative value of that evidence.