Beware the bias of experts: Thomson Rogers’ partner, Robert Ben

This article was produced in partnership with Thomson Rogers.

The exclusion of expert opinion evidence at trial for bias, while rare, is an issue that all lawyers should be aware of, according to Robert Ben, a respected personal injury partner at Thomson Rogers.

The case of Denman v. Radovanovic et al, 2022 ONSC 4401, a recent medical malpractice case brought by his firm, the merits of which remain under reserve by the court and may be subject to appeal, serve as a reminder of this fact, wherein an expert witness for the defence was not permitted to testify because of bias.

 According to Ben, “Historically, when courts have had to contend with an expert witness who might show indications of lacking independence or impartiality, that potential bias would go to the weight of the expert’s opinion, not its admissibility; however, on the particular facts of this case, the judge effectively found the expert was unable to fulfill his duty to the court and that his opinion should not be admitted at all.” To give a sense of how rarely this happens, the judge stated that it was the first time in 18 years she had taken that step.

The case concerned a Thomson Rogers client who suffered a massive brain bleed as a consequence of a pre-surgical embolization procedure. The procedure was part of a multi-step course of elective, non-urgent treatment for a large, previously unruptured, asymptomatic, brain arteriovenous malformation (“AVM”).  The case concerned whether the plaintiff had given informed consent.

When the court lacks specialized knowledge about certain subject matter relevant to the disposition of a case, it relies on expert opinions for assistance. Expert opinions often carry significant weight particularly in complex medical malpractice cases. For that reason, Ben says, everyone should be alert to the dangers of undetected bias in an expert’s opinion

Ben cites a Manitoba Law Journal article by Jason Chin, Michael Lutsky, and Itiel Dror (The Biases of Experts: An Empirical Analysis of Expert Witness Challenges, 2019 CanLIIDocs 2802) that considers the cognitive scientific research on the biases of experts. In the article, Chin notes that the vast majority of experts believe they can overcome bias through mere willpower. This seems to agree with the findings of a 2017 global survey of forensic scientists that showed many experts may have bias blind spots: 71% agreed that expert bias was a concern, yet only 26% allowed that it was a problem for them.

Bias can distort judgment, often unconsciously. Bias can take many forms. There is, for example, relationship/association bias – being assigned a “side” (even at random) can unconsciously bias one toward that side. Tangible reward, such as a financial stake in the outcome of a case (including an expert’s desire for a future retainer) may create bias in favour of one side. Pre-existing views/selection bias, where experts are selected by a party because they have a particular view on an issue which may diverge from the general consensus but align with a party’s theory of the case, can inject bias into a case. Contextual bias can arise where a particular case has emotional facts that may have an impact on an expert’s opinion. Bias can also cascade or snowball, for example where an expert is influenced by a biased theory or conclusion of another expert involved in the case, compounding the original bias.

In White Burgess v. Abbott, 2015 SCC 23, the Supreme Court of Canada confirmed the preferred approach to the problem of expert bias: before an expert can testify, they must be willing and able to carry out their duty to the court. “The acid test,” according to Ben, “is whether the expert’s opinion would not change regardless of which party retained him or her.”

Ben refers to the case of Wise v. Abbott Laboratories, Limited, 2016 ONSC 7275, as instructive. There, the court held that relevant expert evidence is only to be excluded in clear cases of bias. The party alleging bias has to show there is a realistic concern that the expert is unable or unwilling to comply with their duty to the court. The court outlined 14 factors to consider, including: whether the expert has made public statements regarding the case or evidencing hostility toward a particular subject; has a history of exclusive plaintiff or defence retainers; has a long association or personal involvement with a party or lawyer; derives a significant percentage of their income from court appearances; has demonstrated in other cases they lack objectivity and impartiality; proffers unexplained differing opinions on  near identical subject matter in various court appearances or reports;  departs from governing codes or protocols in their field of expertise; persistently fails to recognize other explanations or a range of opinion; bases their opinion on unstated assumptions; and, comes to conclusions that do not remotely relate to the factual foundation or prevailing special knowledge. 

Ben says that “When an expert does not even acknowledge that their opinion may vary depending on the facts, if they're very rigid about their opinion, that may indicate bias to the court.”

In the Denman case, the judge found the defence expert to have violated 8 of the 14 Wise factors and thereby lacked impartiality and was unable to comply with his duty to the court. Among other things, the judge found the expert admitted to an unwillingness to testify for plaintiffs in medical malpractice matters involving standard of care; had a pre-existing relationship with one of the defendants and was willing to provide an opinion regarding his friend, teacher and professional co-collaborator, none of which was disclosed in his report; made credibility findings about the defendant’s evidence effectively accepting their version of events uncritically; in a previous case testified about risk level at odds with his evidence in Denman, which the judge found to be a “pick and choose” opinion favouring the defence; and, significantly departed from the literature-established risk in his opinion.

“The case,” which was heard last summer and is still waiting a ruling and may be subject to appeal, says Ben, “illustrates that although exclusion of expert evidence remains rare, it's still something that is or should be on the radar of every lawyer.”