Where the Crown relies on evidence of a complainant's behavioural change as corroborative of sexual abuse, and the chain of reasoning involves a complicated psychological process, expert evidence is required and the evidence is not within the ordinary experience and knowledge of lay people. The prosecution must lead evidence from the complainant about the behavioural change if it is central to the Crown case; it cannot be assumed the complainant would give evidence supporting the Crown's theory. Evidence of behavioural change given in terms of opinion and conclusion rather than factual description is inadmissible.
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