It is not a condition of admissibility of expert opinion evidence under s 79 of the Evidence Act 1995 (NSW) that the tendering party prove the truth of the assumptions on which the opinion is based; the condition is that the reasoning process be exposed so the tribunal of fact can evaluate the opinion. Where an expert concedes the possibility that an essential element of the offence has not been established, the verdict on that element cannot stand. The question of whether assumptions are proved goes to weight, not admissibility.
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