Westerhof v. Gee Estate, 2015 ONCA
Rule 53.03 applies to situations in which experts are being retained by a party for purposes of the litigation. The Rule does not apply to a participant expert.
A participant expert
i) has special expertise and is giving an opinion based on the witness' observation of or participation in the events at issue; and
ii) formed the opinion as part of the ordinary exercise of the witness's skill, knowledge, training and expertise while observing or participating in the events.
A treating physician is an example of a participant expert. That physician has formed an opinion of the issue not because the physician was asked by a party to testify, but because the physician had already documented the opinion in notes or summaries while treating a party.
The Rule also does not apply to the opinion of a non-party expert. A non-party expert forms an opinion based on personal observations or examinations relating to the subject matter of the litigation, but for purposes other than the litigation. A physician retained by an insurer not involved in the litigation (e.g. a statutory accident benefits insurer) is an example of a non-party expert
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