On May 19, 2021, Paul was a panellist at the Medical Legal Society of Toronto’s program “Medico-Legal Report Part Two: Getting Past the GateKeeper.” The panel brought together lawyers and judges, including the Honourable Justice Todd J. Archibald and the Honourable Justice Mark Edwards, to discuss the role of trial judges as gatekeepers of expert opinion evidence.
The topic is durably relevant. In any case where the outcome turns on expert evidence (and that is almost every medical malpractice trial in Ontario), the trial judge’s gatekeeping decisions can determine whether the plaintiff’s theory of the case is ever put to the trier of fact.
The two-step admissibility framework
The Supreme Court of Canada’s decision in White Burgess Langille Inman v Abbott and Haliburton Co., 2015 SCC 23, sets out the modern framework for admitting expert opinion evidence in civil trials. The framework has two steps.
The first is the threshold inquiry drawn from R v Mohan, [1994] 2 SCR 9. The court asks whether the evidence is relevant, whether it is necessary to assist the trier of fact, whether the expert is properly qualified, and whether the evidence is caught by any exclusionary rule. Evidence that fails any of these threshold requirements is inadmissible.
The second step is discretionary. Even where the threshold test is met, the trial judge weighs the probative value of the proposed evidence against the risks it poses to the trial process, including the risks of consuming court time, of confusing the jury, and of admitting an opinion that lacks the independence and impartiality required of an expert witness. This is the gatekeeping function in the strict sense, and it is the step at which evidence that looks admissible on the surface can still be excluded.
Independence and impartiality
White Burgess clarified that the duties of an expert witness, namely to provide fair, objective, and non-partisan opinion evidence to the court, go to admissibility, not merely to weight. At the threshold, a signed acknowledgment of the expert’s duty (Form 53) will usually be sufficient. If the opposing party challenges admissibility on the basis of bias or lack of independence, the burden shifts back to the party tendering the evidence to establish, on a balance of probabilities, that the expert is able and willing to comply with the duty.
The practical consequence is that the expert’s prior conduct in other cases, the expert’s relationship to a party or to counsel, and the tone and content of the report itself can all become live issues at the gatekeeping stage. An expert whose report reads as advocacy, whose qualifications are stretched to reach beyond their core specialty, or whose disclosure of literature or sources is incomplete is at risk of exclusion before testimony begins.
Rule 53.03 and counsel-expert communications
Rule 53.03 of the Rules of Civil Procedure sets out the procedural requirements for litigation experts in Ontario civil trials. The rule requires service of the expert’s report within fixed timelines, identification of the expert’s qualifications and instructions, disclosure of the literature relied on, and the Form 53 acknowledgment.
A recurring issue at trial is whether counsel’s involvement in shaping the expert’s report has compromised the expert’s independence. The Court of Appeal addressed this directly in Moore v Getahun, 2015 ONCA 55. The court rejected the view that counsel must avoid communication with the expert during the drafting process. Counsel play a mediating role, explaining the legal questions and ensuring that the report is responsive to the issues. The line is between assistance and interference. Communication that shapes the expert’s opinion is improper; communication that ensures the report addresses the right questions in comprehensible terms is not.
The decision did not collapse all the protections around the expert’s independence. Draft reports and communications can still be ordered produced if there is a reasonable foundation to suspect that counsel improperly influenced the substance of the opinion. The practical effect is that counsel-expert communications should be handled with care, but they are not, in themselves, a basis for excluding the resulting report.
Common reasons reports are attacked at trial
Beyond the structural admissibility framework, the recurring practical attack points on a plaintiff’s expert evidence include the following. The expert’s qualifications are tested as not extending to the precise specialty or sub-specialty in issue. The report is challenged as advocacy rather than independent opinion. The Rule 53.03 disclosure of literature and instructions is challenged as incomplete. The expert’s prior involvement with the case (for example, as a treating physician or as a participant in an earlier proceeding) is challenged as compromising independence. The expert is challenged as offering opinion on matters beyond the four corners of the report.
Each of these issues can be addressed at the report-drafting stage, often months or years before trial. They are far harder to address mid-trial in front of a jury.
Practical observations
Getting past the gatekeeper is not a single event at trial. It is the cumulative result of decisions made at the moment the expert is retained, the moment the report is commissioned, the moment the literature is selected, the moment the report is drafted and revised, and the moment defence counsel signal the basis of their challenge. By the time a voir dire is called or a motion to exclude is filed, the work that determines the outcome has largely been done.
The plaintiff who has built the expert evidence with the gatekeeping framework in mind, and whose expert has internalized the duty to the court, is the plaintiff whose case is most likely to be heard on the merits.
