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This case addresses the admissibility of expert evidence. Specifically, it considers whether Rule 53.03 of the Rules of Civil Procedure applies to all expert witnesses or only those who are retained for the purpose of preparing for litigation. This case is relevant for family law proceedings because rule 53.03 is reproduced in Rule 20.1 of the Family Law Rules.


The Ontario Court of Appeal heard two appeals together regarding the admissibility of expert evidence. Both cases were civil cases regarding motor vehicle accidents.

At the jury trial of Westerhof v Gee Estate, the trial judge ruled that opinion evidence from various medical practitioners who had treated the plaintiff after the car accident was inadmissible. Although the jury awarded the plaintiff $22,000 for general damages and $12,000 past loss of income, the trial judge dismissed the action. The plaintiff appealed the judge's decision on the basis that the judge had an incorrect interpretation of Rule 53.03, which resulted in the exclusion of highly relevant and persuasive expert testimony. The Divisional Court affirmed the trial decision. The plaintiff successfully appealed to the Ontario Court of Appeal.

In McCallum v Baker, the trial judge permitted medical practitioners who had treated the plaintiff after the car accident to give opinion evidence regarding the plaintiff's future employment prospects and future treatment needs. A jury awarded the plaintiff $785,275, which largely compensated him for future loss of income and future care. The defendant appealed the decision on the basis that the experts failed to comply with rule 53.03 and their evidence went beyond the scope of their expertise. The Ontario Court of Appeal dismissed the defendant's appeal and affirmed the trial award.


In 2010, the Rules of Civil Procedure were amended to include new provisions regarding expert evidence. Rule 4.1.01 sets out the overriding duty of an expert to provide evidence that is fair, objective and non-partisan, and within the expert's area of expertise. This rule applies to "every expert engaged by or on behalf of a party."

Rule 53.03(2.1) was also added. It specifies the information that must be included in an expert's report, including the expert's name, address and area of expertise; the expert's qualifications and employment and educational experiences in his or her area of expertise; the instructions provided to the expert in relation to the proceeding; the nature of the opinion being sought and each issue in the proceeding to which the opinion relates; and an acknowledgement of expert's duty (Form 53) signed by the expert.

The Court of Appeal found that rule 53.03 only applies to "litigation experts," experts that have been engaged by or on behalf of a party to the litigation. The trial judge in Westerhof erroneously applied rule 53.03 to "participant experts" and "non-party experts."

In earlier case law, participant experts have been referred to as "fact witnesses" because their evidence is derived from their observations of or involvement in the underlying facts of the case. The Court of Appeal prefers the term participant expert because "fact witness" does not make clear whether the witness's evidence must relate only to their observations of the underlying facts or whether they may give opinion evidence admissible for its truth (paragraph 61).

A non-party expert is someone who is retained by a non-party to the litigation and forms an opinion based on personal observations or examinations relating to the subject matter of the litigation, for a purpose other than the litigation (for example, a statutory accident benefits insurer).

Participant experts and non-party experts do not form their opinion for the purpose of litigation, nor are they "engaged to provide evidence in relation to a proceeding" simply by being called to testify for an opinion already formed.

At paragraph 60, the Court concluded the following:

"a witness with special skill, knowledge, training, or experience who has not been engaged by or on behalf of a party to the litigation may give opinion evidence for the truth of its contents without complying with rule 53.03 where:

  • the opinion to be given is based on the witness's observation of or participation in the events at issue; and
  • the witness formed the opinion to be given as part of the ordinary exercise of his or her skill, knowledge, training and experience while observing or participating in such events."

A court still retains its gatekeeper function in relation to opinion evidence from participant experts and non-party experts. For example, if the evidence does not meet the test for admissibility because it goes beyond the scope of an opinion formed in the course of treatment or observations for purposes other than the litigation, then the court may exclude all or part of this evidence or require the expert to comply with rule 53.03.

The purpose of the 2010 amendments were to address several problems related to litigation experts including "the proliferation of experts and expert reports, resulting in an "industry" of competing experts and associated increases in costs; expert bias; lengthy and uncontrolled expert testimony; ... and lack of regulation of the standard content of expert reports" (paragraph 78-79). Participant experts and non-party experts, whose evidence is relevant because of their observation of or participation in events underlying the litigation, was not intended to be affected by the amendments to the Rules.

In McCallum, the Court of Appeal found that the trial judge did not err in allowing the medical practitioners to give their opinions with respect to future medication requirements and the opinions concerning the ability to return to work. The appeal was dismissed.

In Westerhoff, the Court of Appeal found that the trial judge erred in applying rule 53.03, which resulted in the exclusion of important evidence that could have reasonably affected the outcome at trial. Accordingly, a new trial was ordered.