To Comply or Not to Comply? When Experts Fall Outside the Scope of Rule 53.03

On March 26, 2015, the Ontario Court of Appeal released its decision in Westerhof v. Gee Estate concurrently with its companion case McCallum v. Baker[1]. Both decisions were heard at the same time as Moore v. Getahun[2] and, together, form what has been referred to as the Expert Evidence Trilogy (“Trilogy”).

There was an exceptional degree of interest by the Ontario bar in the Trilogy, with six parties intervening in the appeals: The Advocates’ Society; The Holland Group; the Ontario Trial Lawyers Association; the Canadian Defence Lawyers Association; the Canadian Institute of Chartered Business Valuators and the Criminal Lawyers’ Association. Facta of the parties and all interveners are available here. Our coverage of the Moore v. Getahun decision, which was released earlier this year, is available here.

In Westerhof, the Court considered the admissibility of opinions of certain medical witnesses in the context of the Rule 53 regime. The same legal issues were before the court in McCallum. The question on appeal was: to whom does Rule 53 apply?

Rules 53, which came into effect in January 2010, imposes a duty on experts to be independent and impartial. The rule also sets out specific information that must be contained within an expert’s report and it also requires an expert to sign a form acknowledging their duties to the court.

The Court of Appeal has confirmed that Rule 53 applies only to “expert witnesses engaged by or on behalf of a party to provide opinion evidence in relation to a proceeding” and not to treating health care practitioners or other witnesses with special expertise who give opinion evidence who are not “engaged by or on behalf of a party.”


In Westerhof, the plaintiff was injured in a 2004 motor vehicle accident, following which he was treated by a number of health professionals ranging from his family doctor to chiropractors and kinesiologists. At trial, the plaintiff proposed to call a number of these treating health professionals as witnesses. The trial judge excluded or restricted much of this evidence, ruling that medical witnesses who had treated or assessed the plaintiff could not give opinion evidence concerning their diagnosis or prognosis because they had not complied with rule 53.03. The action was dismissed.

To the contrary, in McCallum, the trial judge allowed treating medical practitioners who were not rule 53.03 compliant to give “an avalanche” of opinion evidence that went beyond their direct involvement in the treatment of the patient. These included opinions regarding Mr. McCallum’s ability to return to work and the need for future medication and treatment, as well as prognosis. The court found in favour of Mr. McCallum.

The Divisional Court Decision in Westerhof

Mr. Westerhof appealed to the Divisional Court in 2013. The Divisional Court affirmed the trial judge’s evidentiary rulings. Focusing on the nature of the proffered evidence (is it fact-based evidence, for which no special expertise is required, or opinion evidence, for which it is?) rather than the identity of the witness (who retained them and for what purpose), the Court held:

"The important distinction is not in the role or involvement of the witness, but in the type of evidence sought to be admitted. If it is opinion evidence, compliance with rule 53.03 is required; if it is factual evidence, it is not."

In so holding, the Court departed from a long line of authority which established that opinion evidence from “fact witnesses” is admissible (without Rule 53 compliance) where the opinion evidence is limited to the witness’ involvement, or where the proposed testimony is intended to explain the facts that the witness perceived. Such opinion evidence could include the diagnosis of a treating physician or the imaging report of a radiologist.

The Appeal Decision

The Court of Appeal strongly disagreed with the Divisional Court’s assessment that it is the type of evidence – whether fact or opinion – that is the key factor in determining whether rule 53.03 applied and opted for a general principle permitting two-classes of witnesses to provide opinion evidence without complying with 53.03.

The first class of witnesses, “participant experts” (i.e., witnesses with special skill, knowledge, training or experience and who had observed or were involved in the underlying facts of the case), are permitted to give opinion evidence without compliance where:

  1. the opinion to be given is based on the witness’ observation of or participation in the events at issue; and,
  2. 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.

The second class of witnesses, “non-party experts” (i.e., experts retained by non-parties to the litigation, such as insurers), are permitted to give opinion evidence without complying with rule 53.03 where the witness has formed a relevant opinion based on personal observations or examinations relating to the subject matter of the litigation for a purpose other than the litigation.

In reaching its conclusion, the Court of Appeal made a number of observations which explained why the Divisional Court’s analysis could not stand. The Court held that prior jurisprudence and the very language of the 2010 amendments, which introduced the current rule 53.03, supported the position that rule 53.03 was not applicable to participant and non-party witnesses. The Court was also satisfied that the Osborne Report, which precipitated the 2010 amendments, did not intend to address participant or non-party experts and sought to focus only on those experts engaged by the parties to the litigation. From a practical perspective, the Court concluded that the Divisional Court’s approach would exacerbate expense and delay by requiring participant and non-party experts to comply with rule 53.03. Finally, the Court was confident that any fears surrounding non-disclosure of participant and non-party experts’ opinions were misguided as these opinions could easily be obtained through the discovery process.

The Court applied the general principle to Westerhof, allowed the appeal, and concluded that a new trial was required as important evidence was excluded that could reasonably have affected its outcome.

In applying the general principle to McCallum, the Court was satisfied that the trial judge did not err in failing to exclude some opinion evidence given by participant experts. The Court therefore dismissed the McCallum appeal.

Potential Significance of the Decision

The Court of Appeal’s decision in Westerhof clarifies the analysis that parties ought to conduct when deciding whether a particular opinion witness must comply with rule 53.03. The Westerhof decision and the Trilogy, more broadly, will undoubtedly be of general importance to all trial counsel and of particular importance to counsel practicing in the personal injury field.

While the Court has accepted that participant and non-party experts will not need to comply with rule 53.03 in certain circumstance, it has still not gone so far as to say that compliance will never be required. The Court’s decision has not eliminated future debates about when rule 53.03 compliance ought to be insisted upon by trial courts.

Notably, when considering the McCallum appeal, the Court seems to have recognized that some participant expert opinions (such as opinions concerning a plaintiff’s ability to return to work) will be more difficult to assess. The Court, though concerned about forward looking opinions of this nature, was satisfied in the case before it, that the trial judge did not err in permitting such opinion evidence on the theory that the opinions were disclosed, “appear to have been formed at the time of, and arise directly from, the practitioners’ treatment of [the plaintiff],” and “are not complex vocational opinions requiring highly specialized expertise.”[3]

While the Court was satisfied that such evidence was, in the circumstances of the McCallum trial, permissible without complying with rule 53.03, the Court’s decision leaves open the question of where the line between participant expert and litigation expert is to be drawn. One can easily conceive of instances in which participant experts may be asked by litigation counsel to opine on a matter which, though informed by a participant expert’s observations, may not have otherwise been formulated in the ordinary exercise of the participant expert’s skill, knowledge, training and experience during treatment.


[1] Westerhof v. Gee Estate, 2015 ONCA 206.

[2] Moore v. Getahun, 2015 ONCA 55.

[3] Westerhof v. Gee Estate, 2015 ONCA 206 at para. 165.

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