Expert opinion evidence must satisfy a comprehensive set of requirements to be admissible and carry weight: the field of specialised knowledge must be identified; the witness must demonstrate expertise by reason of specified training, study or experience; the opinion must be wholly or substantially based on that expert knowledge; facts observed must be identified and proved by the expert, and assumed facts must be identified and proved otherwise; the facts must form a proper foundation for the opinion; and critically, the expert must explain how the specialised knowledge applies to the facts to produce the opinion. If these matters are not made explicit, the evidence is either inadmissible or of diminished weight. A court is not bound to accept uncontradicted expert evidence, particularly on ultimate issues.
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