Expert evidence

Today's Court of Appeal decision in R. v. Abbey, 2009 ONCA 624 significantly clarifies the law relating the expert evidence. The Court has materially changed the law and it may well be the case will go on to the Supreme Court -- certainly the Mohan test has been reinterpreted. It is a decision of great importance and ought to be read carefully by all counsel:

[71] It is fundamental to the adversary process that witnesses testify to what they saw, heard, felt or did, and the trier of fact, using that evidentiary raw material, determines the facts. Expert opinion evidence is different. Experts take information accumulated from their own work and experience, combine it with evidence offered by other witnesses, and present an opinion as to a factual inference that should be drawn from that material. The trier of fact must then decide whether to accept or reject the expert's opinion as to the appropriate factual inference. Expert evidence has the real potential to swallow whole the fact-finding function of the court, especially in jury cases. Consequently, expert opinion evidence is presumptively inadmissible. The party tendering the evidence must establish its admissibility on the balance of probabilities: Paciocco & Stuesser at pp. 184, 193; S. Casey Hill et al., McWilliams' Canadian Criminal Evidence, 4th ed., looseleaf (Aurora, Ont.: Canada Law Book, 2009), at para. 12:30.10.

[72] The increased reliance on expert opinion evidence by both the Crown and defence in criminal matters is evident upon even a cursory review of the reported cases. Sometimes it seems that a deluge of experts has descended on the criminal courts ready to offer definitive opinions to explain almost anything. Expert evidence is particularly prevalent where inferences must be drawn from a wide variety of human behaviour: see, for example, R. v. McIntosh (1997), 35 O.R. (3d) 97 (C.A.), at pp. 101-103, leave to appeal to S.C.C. refused R. v. McCarthy, [1998] 1 S.C.R. xii [leave sought by second appellant in McIntosh, Mr. McCarthy]; David M. Paciocco, "Coping With Expert Evidence About Human Behaviour" (1999) 25 Queen's L.J. 305, at pp. 307-308; S. Casey Hill et al. at para. 12:30.10; R. v. Olscamp (1994), 95 C.C.C. (3d) 466 (Ont. Ct. (Gen. Div.)), approved in R. v. Lance (1998), 130 C.C.C. (3d) 438 (Ont. C.A.), at para. 24; Ontario, The Commission on Proceedings Involving Guy Paul Morin: Report, vol. 1 (Toronto: Queen's Printer, 1998), at pp. 311-24. As Moldaver J.A. put it in R. v. Clark (2004), 69 O.R. (3d) 321 (C.A.), at para. 107, a case involving the proposed expert evidence of a criminal profiler:

Combined, these two concerns [giving expert evidence more weight than it deserves and accepting expert evidence without subjecting it to the scrutiny it requires] raise the spectre of trial by expert as opposed to trial by jury. That is something that must be avoided at all costs. The problem is not a new one but in today's day and age, with proliferation of expert evidence, it poses a constant threat. Vigilance is required to ensure that expert witnesses like Detective Inspector Lines are not allowed to hijack the trial and usurp the function of the jury. [Emphasis added.]

[73] Despite justifiable misgivings, expert opinion evidence is, of necessity, a mainstay in the litigation process. Put bluntly, many cases, including very serious criminal cases, could not be tried without expert opinion evidence. The judicial challenge is to properly control the admissibility of expert opinion evidence, the manner in which it is presented to the jury and the use that the jury makes of that evidence.

[74] The current approach to the admissibility of expert opinion evidence was articulated by Sopinka J. in Mohan. Broadly speaking, Mohan replaced what had been a somewhat laissez faire attitude toward the admissibility of expert opinion evidence with a principled approach that required closer judicial scrutiny of the proffered evidence. After Mohan, trial judges were required to assess the potential value of the evidence to the trial process against the potential harm to that process flowing from admission.

[75] The four criteria controlling the admissibility of expert opinion evidence identified in Mohan have achieved an almost canonical status in the law of evidence. No judgment on the topic seems complete without reference to them. The four criteria are:

q relevance;

q necessity in assisting the trier of fact;

q the absence of any exclusionary rule; and

q a properly qualified expert.

[76] Using these criteria, I suggest a two-step process for determining admissibility. First, the party proffering the evidence must demonstrate the existence of certain preconditions to the admissibility of expert evidence. For example, that party must show that the proposed witness is qualified to give the relevant opinion. Second, the trial judge must decide whether expert evidence that meets the preconditions to admissibility is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to the trial process that may flow from the admission of the expert evidence. This "gatekeeper" component of the admissibility inquiry lies at the heart of the present evidentiary regime governing the admissibility of expert opinion evidence: see Mohan; R. v. D.D., [2000] 2 S.C.R. 275; J.-L.J.; R. v. Trochym, [2007] 1 S.C.R. 239; K. (A.); Ranger; R. v. Osmar (2007), 84 O.R. (3d) 321 (C.A.), leave to appeal to S.C.C. refused (2007), 85 O.R. (3d) xviii.

[77] I appreciate that Mohan does not describe the admissibility inquiry as a two-step process. It does not distinguish between what I refer to as the preconditions to admissibility and the trial judge's exercise of the "gatekeeper" function. My description of the process as involving two distinct phases does not alter the substance of the analysis required by Mohan. In suggesting a two-step approach, I mean only to facilitate the admissibility analysis and the application of the Mohan criteria.

[78] It is helpful to distinguish between what I describe as the preconditions to admissibility of expert opinion evidence and the performance of the "gatekeeper" function because the two are very different. The inquiry into compliance with the preconditions to admissibility is a rules-based analysis that will yield "yes" or "no" answers. Evidence that does not meet all of the preconditions to admissibility must be excluded and the trial judge need not address the more difficult and subtle considerations that arise in the "gatekeeper" phase of the admissibility inquiry.

[79] The "gatekeeper" inquiry does not involve the application of bright line rules, but instead requires an exercise of judicial discretion. The trial judge must identify and weigh competing considerations to decide whether on balance those considerations favour the admissibility of the evidence. This cost-benefit analysis is case-specific and, unlike the first phase of the admissibility inquiry, often does not admit of a straightforward "yes" or "no" answer. Different trial judges, properly applying the relevant principles in the exercise of their discretion, could in some situations come to different conclusions on admissibility.

[80] In what I refer to as the first phase, four preconditions to admissibility must be established, none of which were in dispute at trial:

q the proposed opinion must relate to a subject matter that is properly the subject of expert opinion evidence;

q the witness must be qualified to give the opinion;

q the proposed opinion must not run afoul of any exclusionary rule apart entirely from the expert opinion rule; and

q the proposed opinion must be logically relevant to a material issue.

[81] For the purpose of explaining the analytic distinction I draw between the preconditions to admissibility and the "gatekeeper" function, I need not address the first three preconditions. The relevance criterion, however, does require some explanation. Relevance is one of the four Mohan criteria. However, I use the word differently than Sopinka J. used it in Mohan.

[82] Relevance can have two very different meanings in the evidentiary context. Relevance can refer to logical relevance, a requirement that the evidence have a tendency as a matter of human experience and logic to make the existence or non-existence of a fact in issue more or less likely than it would be without that evidence: J.-L.J. at para. 47. Given this meaning, relevance sets a low threshold for admissibility and reflects the inclusionary bias of our evidentiary rules: see R. v. Clark (1999), 129 C.C.C. (3d) 1 (Ont. C.A.), at p. 12. Relevance can also refer to a requirement that evidence be not only logically relevant to a fact in issue, but also sufficiently probative to justify its admission despite the prejudice that may flow from its admission. This meaning of relevance is described as legal relevance and involves a limited weighing of the costs and benefits associated with admitting evidence that is undoubtedly logically relevant: see Paciocco & Stuesser at pp. 30-35.

[83] The relevance criterion for admissibility identified in Mohan refers to legal relevance. To be relevant, the evidence must not only be logically relevant but must be sufficiently probative to justify admission: see Mohan at pp. 20-21; K. (A.) at paras. 77-89; Paciocco & Stuesser at pp. 198-99.

[84] When I speak of relevance as one of the preconditions to admissibility, I refer to logical relevance. I think the evaluation of the probative value of the evidence mandated by the broader concept of legal relevance is best reserved for the "gatekeeper" phase of the admissibility analysis. Evidence that is relevant in the sense that it is logically relevant to a fact in issue survives to the "gatekeeper" phase where the probative value can be assessed as part of a holistic consideration of the costs and benefits associated with admitting the evidence. Evidence that does not meet the logical relevance criterion is excluded at the first stage of the inquiry: see e.g. R. v. Dimitrov (2003), 68 O.R. (3d) 641 (C.A.), at para. 48, leave to appeal to S.C.C. refused (2004), 70 O.R. (3d) xvii.

[85] My separation of logical relevance from the cost-benefit analysis associated with legal relevance does not alter the criteria for admissibility set down in Mohan or the underlying principles governing the admissibility inquiry. I separate logical from legal relevance simply to provide an approach which focuses first on the essential prerequisites to admissibility and second, on all of the factors relevant to the exercise of the trial judge's discretion in determining whether evidence that meets those preconditions should be received.

[86] As indicated above, it was not argued that Dr. Totten's evidence did not meet the preconditions to admissibility. Nor is it suggested that it was not logically relevant to identity, a fact in issue. The battle over the admissibility of his evidence was fought at the "gatekeeper" stage of the analysis. At that stage, the trial judge engages in a case-specific cost-benefit analysis.

[87] The "benefit" side of the cost-benefit evaluation requires a consideration of the probative potential of the evidence and the significance of the issue to which the evidence is directed. When one looks to potential probative value, one must consider the reliability of the evidence. Reliability concerns reach not only the subject matter of the evidence, but also the methodology used by the proposed expert in arriving at his or her opinion, the expert's expertise and the extent to which the expert is shown to be impartial and objective.[8]

[88] Assessment of the reliability of proffered expert evidence has become the focus of much judicial attention, particularly where the expert advances what is purported to be scientific opinion: see, for example, Daubert v. Merrell Dow Pharmaceuticals Inc., 509 U.S. 579 (1993); J.-L.J. at paras. 33-37; S. Casey Hill et al. at para. 12:30.20.30; Bruce D. Sales & Daniel W. Shuman, Experts in Court Reconciling Law, Science, and Professional Knowledge (Washington, D.C.: American Psychological Association, 2005).

[89] In assessing the potential benefit to the trial process flowing from the admission of the evidence, the trial judge must intrude into territory customarily the exclusive domain of the jury in a criminal jury trial. The trial judge's evaluation is not, however, the same as the jury's ultimate assessment. The trial judge is deciding only whether the evidence is worthy of being heard by the jury and not the ultimate question of whether the evidence should be accepted and acted upon.

[90] The "cost" side of the ledger addresses the various risks inherent in the admissibility of expert opinion evidence, described succinctly by Binnie J. in J.-L.J. at para. 47 as "consumption of time, prejudice and confusion". Clearly, the most important risk is the danger that a jury will be unable to make an effective and critical assessment of the evidence. The complexity of the material underlying the opinion, the expert's impressive credentials, the impenetrable jargon in which the opinion is wrapped and the cross-examiner's inability to expose the opinion's shortcomings may prevent an effective evaluation of the evidence by the jury. There is a risk that a jury faced with a well presented firm opinion may abdicate its fact-finding role on the understandable assumption that a person labelled as an expert by the trial judge knows more about his or her area of expertise than do the individual members of the jury: J.-L.J. at para. 25.

[91] In addition to the risk that the jury will yield its fact finding function, expert opinion evidence can also compromise the trial process by unduly protracting and complicating proceedings. Unnecessary and excessive resort to expert evidence can also give a distinct advantage to the party with the resources to hire the most and best experts - often the Crown in a criminal proceeding.

[92] All of the risks described above will not inevitably arise in every case where expert evidence is offered. Nor will the risks have the same force in every case. For example, in this case, I doubt that the jury would have difficulty critically evaluating Dr. Totten's opinion. There was nothing complex or obscure about his methodology, the material he relied on in forming his opinion or the language in which he framed and explained his opinion. As when measuring the benefits flowing from the admission of expert evidence, the trial judge as "gatekeeper" must go beyond truisms about the risks inherent in expert evidence and come to grips with those risks as they apply to the particular circumstances of the individual case.

[93] The cost-benefit analysis demands a consideration of the extent to which the proffered opinion evidence is necessary to a proper adjudication of the fact(s) to which that evidence is directed. In Mohan, Sopinka J. describes necessity as a separate criterion governing admissibility. I see the necessity analysis as a part of the larger cost-benefit analysis performed by the trial judge. In relocating the necessity analysis, I do not, however, depart from the role assigned to necessity by the Mohan criteria.

[94] It seems self-evident that an expert opinion on an issue that the jury is fully equipped to decide without that opinion is unnecessary and should register a "zero" on the "benefit" side of the cost-benefit scale. Inevitably, expert opinion evidence that brings no added benefit to the process will be excluded: see, for example, R. v. Batista (2008), 238 C.C.C. (3d) 97 (Ont. C.A.), at paras. 45-47; R. v. Nahar (2004), 181 C.C.C. (3d) 449 (B.C.C.A.), at paras. 20-21. Opinion evidence that is essential to a jury's ability to understand and evaluate material evidence will register high on the "benefit" side of the scale. However, the ultimate admissibility of the opinion, even where it is essential, will depend on not only its potential benefit, but on the potential prejudice to the trial process associated with its admission.

[95] In many cases, the proffered opinion evidence will fall somewhere between the essential and the unhelpful. In those cases, the trial judge's assessment of the extent to which the evidence could assist the jury will be one of the factors to be weighed in deciding whether the benefits flowing from admission are sufficiently strong to overcome the costs associated with admission. In addressing the extent to which the opinion evidence is necessary, the trial judge will have regard to other facets of the trial process -such as the jury instruction - that may provide the jury with the tools necessary to adjudicate properly on the fact in issue without the assistance of expert evidence: D.D. at para. 33; R. v. Bonisteel (2008), 236 C.C.C. (3d) 170 (B.C.C.A.), at para. 69.

[96] It is unnecessary to explore the necessity requirement in any greater detail. The trial judge appears to have accepted defence counsel's concession that Dr. Totten's evidence was necessary in the sense that the meaning of a teardrop tattoo was outside of the ordinary knowledge of a Toronto juror (para. 34).