Canada: Ongoing Uncertainties With Participant Experts

Last Updated: October 12 2018
Article by Stephen G. Ross and Meryl Rodrigues

Over three years have passed since the release of the Ontario Court of Appeal's decision in Westerhof v. Gee Estate1, wherein the Court definitively outlined the role of "participant experts".

In short, the Court noted that participant experts, with special skill, knowledge, training, or experience, who have not been engaged by or on behalf of a party, may give opinion evidence for the truth of its contents, without compliance with Rule 53.03, where the following conditions are met:

  • the opinion to be given is based on the witness' 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.

Despite the passage of time, there does not appear to have been much consideration of the role of participant experts within the framework for the admissibility of expert evidence in general, as outlined most recently by the Supreme Court of Canada in White Burgess Langille Inman v. Abbott and Haliburton Co.2 and subsequently articulated by the Ontario Court of Appeal in R. v. Abbey3.

Admissibility of Expert Evidence

The White Burgess framework sets out threshold criteria for the admissibility of expert evidence, all of which are to be met before the trial judge exercises his or her gatekeeping function in determining whether the benefits of admitting the evidence outweigh the costs of admission.

Arguably, the threshold criteria of logical relevance, necessity, and the absence of the application of an exclusionary rule require no particularly special consideration in the context of participant experts, versus litigation experts subject to Rule 53.03.

However, the same cannot be said of the threshold criterion of proper qualification, which, according to White Burgess and Abbey, requires that the expert be "willing and able to fulfil the expert's duty to the court to provide evidence that is: (i) [i]mpartial, (ii) [i]ndependent, and (iii) [u]nbiased."

The importance of this criterion cannot be overstated. Indeed, considerations of impartiality, independence and bias arise both at the threshold stage and in the gatekeeping stage of the framework.

Moreover, the Supreme Court in White Burgess held that an expert's lack of impartiality and independence and an expert's bias go both to admissibility of the evidence, as well as to the weight it ought to be given if admitted.4

Duty of Participant Experts

Consider these factors as they relate to participant experts. As stated above, participant experts are not subject to Rule 53.03, which requires that an expert acknowledge his or her duty to the court to provide fair, objective and non-partisan opinion evidence, overriding any duty that may be owed to a party (Form 53).

Although the Court in Westerhof did indicate that the court could require a participant expert to comply with Rule 53.03, this was in respect of opinion evidence that may be "beyond the scope of an opinion formed in the course of treatment or observation for purposes other than the litigation."

What of the opinion that is formed in the course of treatment or observation for purposes other than litigation? Surely, only qualified and otherwise impartial and unbiased experts should be permitted to give opinion evidence in court.

However, both pre- and post-Westerhof, it has been commonplace to have a plaintiff's treating doctor testify not only as a fact witness, but also to proffer opinion evidence speaking to diagnosis, treatment and prognosis evidence.5

It seems this has been with little or no regard to the factors of impartiality, independence, and bias underlying admissibility of such opinion evidence, from a medical professional whose duty is, arguably, to his or her patient, and not to the court.

Recent Case

An example may serve to highlight the concerns this should raise. In Imeson v. Maryvale,6 the trial judge permitted the plaintiff's treating psychologist to testify as a participant expert, and to proffer opinions formed as part of the ordinary exercise of his skill, knowledge, training and experience while observing or participating in the events at issue.

While the trial judge acknowledged those limits on the opinions that could be provided by the psychologist, there is no consideration given to a potential lack of impartiality or independence, or to bias – either as a threshold criterion or as a gatekeeping exercise.

It is submitted that concerns relating to impartiality, independence and bias are particularly acute in such a context as that in Imeson.

Ontario courts have recognized that a treating mental health practitioner, who establishes a therapeutic alliance with a patient, faces a challenge being objective and may be considered an advocate for the patient.7

One wonders whether such a treating practitioner can be sufficiently impartial, independent and unbiased, to permit the opinions permissible from participant experts under Westerhof.

Arguably, similar considerations can apply in the context of other treating practitioners, particularly ones with longstanding relationships with the plaintiff. Certainly, at the very least, the issues of impartiality, independence and bias ought to be canvassed before allowing such participant experts to provide their opinions pursuant to the Westerhof guidelines.

The court should be satisfied that, although their first duty in the course of care or treatment with the plaintiff is to the plaintiff, their first duty in the course of testifying at trial is to the court.

Once such baseline impartiality has been both acknowledged and accepted, perhaps the opinion can be tendered, with any remaining reservations regarding partiality, independence or bias going to the weight to be afforded such testimony.


It appears that "participant experts" are here to stay and will be part of the trial landscape for the foreseeable future. It is hoped, however, that, over time, greater clarity will emerge regarding the limits surrounding the admissibility of such opinion evidence.

As indicated, it is the authors' view that the evidence of participant experts should be put at least to the same judicial scrutiny as that applied to the proposed admission of any expert opinion.

White Burgess and Abbey reveal that the threshold admissibility of expert evidence requires impartiality, independence and a lack of bias. It is submitted that no less should be required and expected of participant experts in our courtrooms.


[1] 2015 ONCA 206.

[2] 2015 SCC 23.

[3] 2017 ONCA 640.

[4] Considerations of bias with respect to expert evidence in the criminal context were recently outlined in R.  v. Natsis, 2018 ONCA 425.

[5] See Davies v. The Corporation of the Municipality of Clarington, 2016 ONSC 1079.

[6] 2016 ONSC 6020 – appeal pending.

[7] R v. Brown, 2006 CarswellOnt 2329, aff'd 2007 ONCA 607. See also, R v. K(L), 2011 ONSC 2562.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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