The assessment of whether a witness possesses the specialised knowledge required under s 79 of the Evidence Act 1995 (NSW) is a question of fact, and a finding on that question will not give rise to an appeal on a point of law unless an error of principle is demonstrated. An expert opinion must be presented in a form that makes it possible to determine whether it is wholly or substantially based on the witness's specialised knowledge. Even if an evidential ruling is erroneous, the error must be material to the outcome to warrant appellate intervention.
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