The Court of Appeal overturned the Divisional Court decision, which held that the key factor in determining whether r. 53.03 applies is whether the evidence is fact or opinion. Instead, the Court held:
Rule 53.03 does not apply to the opinion evidence of a non-party expert where that person 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. The court retains its gatekeeper function and may require compliance with r. 53.03 if the expert goes beyond the scope of opinion formed in the course of treatment or observation for purposes outside of the litigation. Instead, I conclude that a witness with special skill, knowledge, training, or experience who has not been engaged by or on behalf of a party to the litigation may give opinion evidence for the truth of its contents without complying with rule 53.03 where:· the opinion to be given is based on the witness’s 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.
Given the decision in Westerhof it will now be permissible for treating practitioners and accident benefits assessors to testify without complying with r. 53.03.