Executive Summary: Key Legal and Evidentiary Issues

• Classification of a long-term treating psychologist as both a participant expert and a Rule 53.03 “litigation expert” in an Ontario jury trial
• Adequacy of three narrative psychological reports, read collectively, to satisfy Rule 53.03(2.1) despite technical deficiencies in individual reports
• Application of s. 12 of the Evidence Act to permitting more than three opinion witnesses and managing potential duplication of psychological expert evidence
• Scope of opinion evidence a participant expert may give where diagnoses and prognoses are not fully set out in contemporaneous clinical notes
• Judicial approach to balancing prejudice, trial efficiency, and the need for relevant expert evidence where objections to expert numbers and status are raised mid-trial
• Assessment of impartiality and independence of a treating psychologist serving in a dual role as participant expert and litigation expert under the White Burgess framework

Factual background

The case arises from a motor vehicle accident that occurred on December 22, 2016, in which the plaintiff, Linda Wallis, alleges significant psychological injury. She has been under the care of a psychologist, Dr. Anne McDermid, since April 2017 and continues to receive treatment almost nine years on from the date of loss. Her treatment has focused on psychological symptoms, functional limitations, and the impact of the accident on her daily life, work capacity, and general well-being. The litigation is a civil jury trial in the Ontario Superior Court of Justice, scheduled as a five-week trial, and the ruling is delivered in its fourth week. The defendants include unidentified drivers (John/Jane Doe and Jack/Jill Doe) as well as The Wawanesa Mutual Insurance Company, which stands as the insurer defendant in the proceeding. The plaintiff’s case centers on the extent of her psychological impairment, causation linking those impairments to the accident, and the practical consequences for her employability and need for ongoing psychological care.

Psychological treatment and expert evidence landscape

Over the course of her treatment, Dr. McDermid maintained clinical notes that mainly recorded the plaintiff’s subjective complaints, therapy discussions, and life stressors, such as housing issues, rather than detailed diagnostic labels or prognostic statements. In addition to her clinical chart, she prepared three narrative reports dated March 2, 2018, February 20, 2025, and February 6, 2026, and also completed an online questionnaire for Ms. Wallis’s disability insurer. The plaintiff’s trial strategy was to call Dr. McDermid as at least a participant expert, and potentially also as a full litigation expert under Rule 53.03, so that she could address diagnosis, prognosis, employability, causation, and future treatment in more formal opinion evidence. By the time of this mid-trial ruling, other expert witnesses had already testified or were expected to testify. On the plaintiff’s side, psychologist Dr. Iezzi and physiatrist Dr. Kumbhare had been called as litigation experts, and an occupational therapist (Ms. Farrell) and an economic loss expert were expected. The plaintiff also intended to rely on reports commissioned by the accident benefits insurer, including a psychological report from non-party expert Dr. Derry. The defence had retained its own neuropsychologist, Dr. Abeare, whose opinion was expressly addressed in both Dr. Iezzi’s second report and Dr. McDermid’s final report. The expert evidence therefore involved overlapping psychological opinions from a treating psychologist and an assessor psychologist, as well as competing causation theories focusing in part on the role of sleep disturbances in cognitive difficulties.

Legal framework for participant and litigation experts

The court analyzed the expert status of Dr. McDermid against the Ontario Court of Appeal’s guidance in Westerhof v. Gee Estate and Imeson v. Maryvale. Under Westerhof, participant experts such as treating physicians may give opinion evidence regarding history, diagnosis, and prognosis formed in the ordinary course of treatment, without complying with Rule 53.03, so long as the opinion is based on their own observations and participation in the underlying events. Imeson confirms that once a treating expert goes beyond those boundaries, the Rule 53.03 regime applies. The trial judge emphasized that a participant expert’s opinions are typically, but not invariably, found in clinical notes and treatment-related reports. A participant expert is not rigidly confined to opinions expressly written down at the time; opinions that can be reliably recalled and are grounded in the contemporaneous treatment can still be given, even if the exact diagnostic phrase was not recorded in a particular note. The court rejected the defence view that a treating expert is barred from expressing a diagnosis or prognosis if those words do not appear verbatim in the records, using a hypothetical example of a cardiologist who records classic heart attack symptoms but omits the term “heart attack” from the note. The key constraint is temporal: the participant expert may testify to opinions formed at the time of treatment (and, in an ongoing treatment relationship, up to the present), not new opinions manufactured later purely for litigation.

Rule 53.03 compliance of the McDermid reports

Turning to the three narrative reports, the judge examined whether, taken together, they met the formal requirements of Rule 53.03(2.1). The first report, dated March 2, 2018, clearly set out the questions posed to the expert, including diagnosis and prognosis, assessment of employability, whether the plaintiff was disabled from her pre-accident or any employment, the anticipated duration of disability, and appropriate timing for re-evaluation. It gave substantive reasons and articulated her opinion without overt signs of advocacy. However, it lacked a statement of qualifications and did not list the documents relied upon, rendering it technically non-compliant in isolation. The second report, dated February 20, 2025, cured many of these gaps by providing a detailed account of the psychologist’s educational and professional background and a list of materials reviewed, including expert reports and a medical brief index. It also dealt with diagnosis, prognosis, employability, and the daily life impact of the accident, again with detailed reasoning and no apparent bias. The third report, dated February 6, 2026, further set out her qualifications and offered a reasoned rebuttal to the defence neuropsychological opinion of Dr. Abeare and addressed the future care recommendations of occupational therapist Ms. Farrell. The expert also signed a Form 53 Acknowledgment of duty to the court. The judge concluded that, read collectively, the reports were sufficiently compliant with Rule 53.03’s purpose of ensuring transparency, avoiding trial by ambush, and enabling the other side to know the case to meet and respond through their own experts. Any technical deficiencies could be addressed on cross-examination, and there was no real prejudice, given that the defence experts had already responded to her opinions in their own reports.

Section 12 of the Evidence Act and expert numbers

The court then addressed s. 12 of the Evidence Act, which provides that no more than three opinion witnesses may be called on each side without leave. The plaintiff had not formally sought leave in advance, though the motion effectively operated as such a request. Prior decisions like Davies v. Clarington and McNamee v. Oickle emphasize concerns about “piling on” duplicative experts, judicial economy, and the need for necessity under the Mohan test when a party seeks more than one expert in the same specialty. There is also a line of authority, including Higashi v. Chiarot, interpreting Davies to mean that pure participant experts do not count towards the three-expert cap, while litigation experts (and participant experts who cross the line into Rule 53 territory) do. Here, the judge accepted that because the plaintiff sought to have Dr. McDermid give full litigation-style opinion evidence as well as participant testimony, it was appropriate to treat her as within the s. 12 framework and therefore consider leave. Several contextual factors informed the exercise of discretion. In Davies and McNamee, objections to expert numbers were made before any experts testified, allowing parties to choose which expert to call. In contrast, the defence’s objection in this case came only on the eve of Dr. McDermid’s testimony, after psychologist Dr. Iezzi had already been called. The court noted that had the plaintiff been forced to choose only one psychologist, she would have called the treating psychologist, not the assessor, given the depth of Dr. McDermid’s long-term knowledge of the plaintiff. The scheduling of witnesses had been driven by practical issues, such as juror problems and expert availability, and there was no real time saving to be had by restricting her to participant-only evidence because she would be testifying regardless. While the court acknowledged some duplication between the opinions of Drs. McDermid and Iezzi, particularly regarding diagnoses of pain-related and depressive disorders, poor prognosis, unemployability, and causation, it saw limited prejudice to the defence. The defence had fully responded to her reports in their own expert evidence, had had ample notice of the content of her opinions, and would have to cross-examine her in any event. In these circumstances, and guided by appellate commentary in Girao v. Cunningham cautioning against excluding relevant evidence unnecessarily, the judge granted leave to the plaintiff to exceed the usual three-expert limit.

Impartiality and the treating psychologist’s dual role

The defence also questioned whether a treating psychologist who has seen the plaintiff for nine years can truly give impartial litigation-style evidence. The judge analyzed this concern under the Supreme Court of Canada’s framework from White Burgess Langille Inman v. Abbott and Haliburton and subsequent Ontario cases such as Taylor v. Zents. Those authorities confirm that a participant expert can be qualified under Rule 53 as long as the court is satisfied that the expert appreciates and can honour the duty to provide fair, objective, and non-partisan evidence. A pre-existing relationship, even a therapeutic or familial one, does not automatically disqualify an expert; the issue is whether the expert is unable or unwilling to rise above that relationship and serve the court first. Here, Dr. McDermid had signed a Form 53, explicitly acknowledging her duty to the court. Her written reports did not read as advocacy pieces and, in the judge’s view, were fair and even-handed in their reasoning. While the court candidly recognized that a doctor-patient relationship inevitably creates some tension with the expert’s duty to the court, it was not prepared to find at the threshold stage that she could not manage that conflict. The judge therefore determined that her impartiality concerns should be addressed through a voir dire at qualification and, if necessary, through the gatekeeper function during her viva voce evidence, including the possibility of limiting or halting her testimony if obvious bias emerged.

Outcome of the mid-trial motion and overall impact

In the result, the court ruled that Dr. McDermid may testify both as a participant expert and as a litigation expert psychologist. She is permitted to give evidence of her diagnosis and prognosis of Ms. Wallis throughout the period of treatment, to speak to employability and causation in line with her three reports, and to address future psychological treatment needs, notably because Dr. Iezzi himself deferred to her on treatment planning. She is also expressly allowed to respond to the defence neuropsychologist’s views, particularly the suggestion that sleep issues largely explain any cognitive impairment, in accordance with her February 6, 2026 report. The judge granted leave under s. 12 of the Evidence Act to allow the plaintiff to call more than three expert witnesses in these circumstances and rejected arguments that the defence would suffer real prejudice from duplication. As this is only a mid-trial evidentiary ruling, it does not resolve liability or quantum of damages in the underlying personal injury and insurance dispute. The only “successful party” identifiable from this decision is the plaintiff, who prevailed on the motion to have her treating psychologist qualified to provide extended expert opinion evidence, but the ruling does not contain any order awarding damages, costs, or other monetary relief; the total financial outcome in favor of any party cannot be determined from this decision alone.