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ARTICLE · 20 SEPTEMBER 2019

Participant Expert Witnesses: What Happens When Litigants Are Also Experts

McKercher LLP
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A participant expert witness has relevant expertise and was involved in the events that underlie the litigation. Participant experts are generally permitted to provide both fact and limited opinion

CanadaLitigation, Mediation & Arbitration
C. Kelsey O’Brien
C. Kelsey O’Brien
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A participant expert witness has relevant expertise and was involved in the events that underlie the litigation. Participant experts are generally permitted to provide both fact and limited opinion evidence. Occasionally, a participant expert is also a litigant.

In Westerhof v Gee Estate, the Ontario Court of Appeal addressed whether the Ontario Rules of Civil Procedure1 relating to expert witnesses also apply to participant experts. The Court noted that participant experts include "treating physicians, who form opinions based on their participation in the underlying events ... rather than because they were engaged by a party to the litigation to form an opinion."

According to Westerhof, a participant witness may give opinion evidence where:

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