Expert Evidence

 Bruff-Murphy v. Gunawardena, 2017 ONCA 502:

 

[34]       In White Burgess, a decision released shortly before the judgment under appeal, the Supreme Court of Canada provided clarity and guidance regarding challenges to experts on the basis of bias and lack of independence. Cromwell J., writing for the court, stated at para. 19 that the basic structure for the law relating to the admissibility of expert evidence has two main components.

[35]       The first component requires the court to consider the four traditional "threshold requirements" for the admissibility of the evidence established in R. v. Mohan, [1994] 2 SCR 9: (i) relevance; (ii) necessity in assisting the trier of fact; (iii) absence of an exclusionary rule; and (iv) the need for the expert to be properly qualified.

[36]       The second component is a "discretionary gatekeeping step" where "the judge balances the potential risks and benefits of admitting the evidence in order to decide whether the potential benefits justify the risks": para. 24. It is a cost-benefit analysis under which the court must determine whether the expert evidence should be admitted because its probative value outweighs its prejudicial effect.

[37]       The analysis under the second component is best thought of as a specific application of the court's general residual discretion to exclude evidence whose prejudicial effect exceeds its probative value: R. v. Bingley, 2017 SCC 12, 407 D.L.R. (4th) 384, at para. 16. As Charron J.A. wrote in R. v. K. (A.) (1999), 45 O.R. (3d) 641 (C.A.), at para. 76, application for leave quashed, [2000] S.C.C.A. No. 16: "The balancing process which lies at the core of the determination of the admissibility of this kind of evidence is not unique to expert opinion evidence. It essentially underlies all our rules of evidence." In White Burgess, Cromwell J. referenced Mohan and made the same point at paras. 19 and 20:

Mohan also underlined the important role of trial judges in assessing whether otherwise admissible expert evidence should be excluded because its probative value was overborne by its prejudicial effect — a residual discretion to exclude evidence based on a cost-benefit analysis: p. 21.

…

The reasons in Mohan engaged in a cost-benefit analysis with respect to particular elements of the four threshold requirements, but they also noted that the cost-benefit analysis could be an aspect of exercising the overall discretion to exclude evidence whose probative value does not justify its admission in light of its potentially prejudicial effects: p. 21.

[38]       Cromwell J. further explained that lack of independence or impartiality on the part of an expert witness goes to the admissibility of the witness's testimony, not just to its weight: para. 40. Specifically, in the governing framework for admissibility, the court should consider an expert's potential bias when determining whether the expert is properly qualified at the initial threshold inquiry: para. 53.

[39]       However, he added that bias should also be considered when the court exercises its gatekeeping exclusionary discretion, writing at para. 54:

Finding that expert evidence meets the basic threshold does not end the inquiry. Consistent with the structure of the analysis developed following Mohan which I have discussed earlier, the judge must still take concerns about the expert's independence and impartiality into account in weighing the evidence at the gatekeeping stage. At this point, relevance, necessity, reliability and absence of bias can helpfully be seen as part of a sliding scale where a basic level must first be achieved in order to meet the admissibility threshold and thereafter continue to play a role in weighing the overall competing considerations in admitting the evidence. At the end of the day, the judge must be satisfied that the potential helpfulness of the evidence is not outweighed by the risk of the dangers materializing that are associated with expert evidence. [Emphasis added.]

In the overview of his discussion of the admissibility of expert opinion evidence, he instructed at para. 34 that:

[A] proposed expert's independence and impartiality go to admissibility and not simply to weight and there is a threshold admissibility requirement in relation to this duty. Once that threshold is met, remaining concerns about the expert's compliance with his or her duty should be considered as part of the overall cost-benefit analysis which the judge conducts to carry out his or her gatekeeping role. [Emphasis added.]

[40]       In the present case, the trial judge cited White Burgess and appears to have relied upon Cromwell J.'s statement that in the threshold inquiry it would be quite rare for a proposed expert's evidence to be ruled inadmissible. As Cromwell J. noted at para. 49, all that needs to be established at that stage is whether the expert is "able and willing to carry out his or her primary duty to the court." The trial judge concluded that Dr. Bail met this rather low threshold requirement.

[41]       That was a discretionary decision, which is entitled to deference from this court: R. v. Shafia, 2016 ONCA 812, 341 C.C.C. (3d) 354, at para. 248. Another judge might well have concluded that Dr. Bail failed to meet even this low threshold test. I do not need to decide whether the trial judge erred on this point, however, because he clearly erred in principle in failing to proceed to the next step of the analysis – consideration of the cost-benefit analysis in Dr. Bail's testimony. The trial judge did not reference this second component of his discretionary gatekeeper role. To the contrary, he appears to have believed that he was obliged to qualify Dr. Bail once he concluded that the witness met the initial Mohan threshold. There is, therefore, no decision to defer to and it falls to this court to conduct the second part of the analysis.