R. v. Shafia, 2016 ONCA 812
The Expert Evidence Two-Step
[226] A two-step inquiry governs the admissibility of expert opinion evidence as an exception to the general rule that excludes evidence of opinion. The first step involves the threshold requirements of admissibility, the second a balancing of potential risks and benefits of admitting the evidence in order to determine whether the potential benefits justify the risks: White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, [2015] 2 S.C.R. 182, at paras. 22-24; Abbey.
The First Step – Threshold Reliability
[227] At the first step, the proponent of the evidence – here, the Crown, - must establish the threshold requirements of admissibility discussed in R. v. Mohan, 1994 CanLII 80 (SCC), [1994] 2 S.C.R. 9, at p. 20:
• relevance
• necessity
• absence of an exclusionary rule
• a duly qualified expert.
See, Abbey, at para. 75. Relevance at this stage refers to logical relevance: White Burgess, at para. 23; Abbey, at para. 82. The expert opinion evidence must 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 the evidence: Abbey, at para. 82; R. v. J.-L.J., 2000 SCC 51, [2000] 2 SCR 600, at para. 47.
[228] The qualifications of an expert are an essential component of the Mohan requirements. The independence and partiality of a proposed expert are relevant to the threshold requirement that the expert be qualified to proffer evidence of opinion on a specified subject: White Burgess, at para. 34.
[229] The application of the Mohan requirements in any proceedings is case-specific. In each case, the trial judge determines issues of relevance and necessity within the factual matrix of the trial in which he or she is presiding. The inquiry is very much a function of the other evidence and issues in the case being tried: R. v. D.(D.), 2000 SCC 43, [2000] 2 S.C.R. 275, at para. 12; R. v. Morin, 1988 CanLII 8 (SCC), [1988] 2 S.C.R. 345, at p. 370.
[230] The case-specific nature of the Mohan inquiry has implications for the standard of appellate review. Appellate review is not precluded, as for example, where a finding of admissibility under Mohan is clearly unreasonable, contaminated by an error in principle or reflective of a material misapprehension of evidence. That said, appellate courts should proceed from a stance of deference to decisions of trial judges to admit or reject expert opinion evidence: D. (D.), at para. 13.
The Second Step: The Cost-Benefit Analysis
[231] The second step – the discretionary gatekeeping step – requires the trial judge to balance the potential risks and benefits of admitting the evidence to decide whether the potential benefits justify the risks: White Burgess, at para. 24; Abbey, at para. 76. This inquiry is equally case-specific. It involves the exercise of judicial discretion, not the application of a bright line rule: Abbey, at para. 79.
[232] The benefit side of this cost-benefit analysis requires a consideration of the probative potential of the evidence, as well as the significance of the issue to which the evidence is directed. Determination of the probative potential of the evidence of necessity requires a consideration of the reliability of the evidence, but not to such an extent as to intrude upon the jury’s task in assessing ultimate reliability: Abbey, at paras. 87-89. The independence of the expert and his or her impartiality are also factors: White Burgess, at para. 54. Opinion evidence essential to a jury’s ability to understand and evaluate material evidence registers high on the “benefit” scale: Abbey, at para. 94.
[233] The “cost” side of the analysis examines the risks inherent in the introduction of expert opinion evidence. Consumption of time. Prejudice. Confusion. Danger that jurors will be unable to make an effective and critical assessment of the evidence. The complexity of the materials. The impenetrable jargon in which the opinion is clothed. Compromise of the trial process by unduly protracting and complicating proceedings: see, Abbey, at paras. 90-92; White Burgess, at para. 54.
[234] The product of the judge’s cost-benefit analysis of expert opinion evidence tendered for admission – the admissibility decision – is entitled to deference on appellate review, at least in the absence of an error in principle or an unreasonable conclusion: D.(D.), at para. 13; Abbey, at para. 97; R. v. Araya, 2015 SCC 11, [2015] 1 S.C.R. 581, at para. 31.
Keeping Expert Opinion Evidence within Proper Bounds
[235] The task of a trial judge asked to admit expert opinion evidence in a criminal trial is not complete with the decision to admit the evidence. The trial judge has an on-going obligation to ensure that the expert witness does not stray beyond his or her identified field of expertise and pollute the trial with opinions beyond the subject-matter of his or her expertise: R. v. M.C. (2014), 2014 ONCA 611, 314 C.C.C. (3d) 336, at para. 75; Abbey, at para. 62; Sekhon, at paras. 46-47; and R. v. Marquard, 1993 CanLII 37 (SCC), [1993] 4 S.C.R. 223, at pp. 242-244.
[236] Three additional points in relation to expert evidence spilling over the boundaries set by the trial judge warrant mention.
[237] First, as a practical matter, it is for opposing counsel to object when the expert ventures an opinion beyond the area of expertise in which she or he has been qualified: Marquard, at p. 244.
[238] Second, when an expert’s opinion exceeds his or her area of qualified expertise, the evidence in excess should be struck if the witness has no expertise in the area, but left for the trier of fact if the failure to qualify in the area was technical or inadvertent: Marquard, at p. 244.
[239] Third, the general remedy where the evidence of an expert exceeds its bounds is a remedial instruction advising the jury to disabuse their minds of the inadmissible portion of the evidence: Sekhon, at para. 48; Marquard, at p. 244.
Cultural Evidence
[240] Expert opinion evidence about cultural mores within particular communities is a well-recognized field of study within the academic and professional disciplines: Abbey, at para. 121. Scientific validity is not a condition precedent to the admissibility of expert opinion evidence. Indeed, the great bulk of expert opinion evidence admitted in our courts is given by experts in disciplines that do not use the scientific method and whose opinions cannot be scientifically validated: Abbey, at para. 109.
[241] Expert opinion evidence about cultural mores may be relevant to and thus admissible on a variety of issues including to provide context for and to facilitate appreciation of other evidence: R. v. Boswell, 2011 ONCA 283, 277 C.C.C. (3d) 156, at para. 26. The evidence may also be admissible to support a defence of provocation and to establish that a murder was planned and deliberate: R. v. Sadiqi, 2013 ONCA 250, at para. 16.
Statistical Evidence of Probabilities
[242] An expert is not entitled to give statistical evidence of probabilities based on prior similar events to support a conclusion about what happened on the occasion that forms the subject-matter of charges: R. v. Klymchuk (2005), 2005 CanLII 44167 (ON CA), 203 C.C.C. (3d) 341 (Ont. C.A.), at para. 46.
Anecdotal Evidence from Experts
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