The Court of Appeal recently released a decision on the role of expert witnesses and the role of the trial judge as gatekeepers of such evidence.
In Bruff-Murphy v. Gunawardena, 2017 ONCA 502, the Court of Appeal considered an appeal from a car accident case. Bruff-Murphy, the appellant, claimed that she suffered physical and mental injuries as a result of a car accident caused by Gunawardena. Gunawardena admitted liability and a 23-day jury trial occurred to determine Bruff-Murphy’s damages. At trial, the jury awarded Bruff-Murphy $23,500.00 in general damages. On appeal, Justices Lauwers, Hourigan, and Benotto overturned the trial decision and ordered a new trial because “the defence proffered the evidence of a wholly unsuitable expert witness” (para. 72).
The expert at issue was a psychiatrist and he was the last witness in the defence’s case. In particular, his expert opinion was that the plaintiff did not develop any psychiatric disorders or limitations as a result of the accident. However, the methodology of his process and the tone of his expert report were found by the Court of Appeal to be more prejudicial than probative. The Court of Appeal was highly critical of how unfair it was for this expert to focus on the inconsistencies between the information that he received from the plaintiff though an interview and the information that he later discovered from reviewing the plaintiff’s medical records without putting these inconsistencies to the plaintiff and giving her the opportunity to explain. The overall tone of the expert report, where the expert went out of his way to make damaging comments to the plaintiff’s case, was also found to be reliable indicator of the expert’s testimony.
While the Court of Appeal appreciated that the trial judge correctly turned his mind to the four traditional criteria for the admissibility of expert evidence as established in R. v. Mohan, the trial judge was found to have erred for failing to weigh the prejudicial effect of this expert’s evidence against it’s probative value as the final step during the qualification stage.
To quote Justice Hourigan at paragraphs 35 and 36 of this decision, the test during the qualification stage is as follows,
 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 CanLII 80 (SCC),  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.
 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.
For those who are interested in the topic of admissibility of expert evidence, click here for the Supreme Court of Canada decision in White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23.
Thanks for reading and stayed tuned for my blog later this week on the trial judge’s gatekeeper role after the qualification stage.