Expert Opinion

The contributions of the expert witness include demystifying, explaining and, in giving an expert opinion, placing the parties and the court in a better position to form judgements as to facts proved in evidence. (1)



The role of the expert is to advance a client’s case, but this must be done within the context that the expert must assist the court impartially on matters relevant to the area of expertise of the witness. (2)

An expert’s ‘duty is to furnish the Judge or jury with the necessary scientific criteria for testing the accuracy of their conclusions, so as to enable the Judge or jury to form their own independent judgment by the application of these criteria to the facts proved in evidence’ (3)

Three rules of evidence to apply to the reception of expert evidence. (4) They are:

  1. the expertise rule: does the witness have knowledge and experience sufficient to entitle them to be held out as an expert who can assist the court?
  2. the area of expertise rule: is the claimed knowledge and expertise sufficiently recognised as credible by others capable of evaluating its theoretical and experiential foundations?
  3. the basis rule: to what extent can an expert’s opinion be based upon matters not directly within the expert’s own observations?

Common law rules of evidence generally render evidence of opinion inadmissible. Section 79 of the Evidence Act 2008 provides that ‘[i]f a person has specialised knowledge based on the person’s training, study or experience, the opinion rule does not apply to evidence of an opinion of that person that is wholly or substantially based on that knowledge’. (5)

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ASI Recent Matters


  1. Davie v Magistrates of Edinburgh [1953] SC 34, 40 (Cooper LP)
  2. Supreme Court (General Civil Procedure) Rules 2005 (Vic) Form 44A – Expert Witness Code of Conduct
  3. Davie v Magistrates of Edinburgh [1953] SC 34
  4. Ibid 40 (Cooper LP)
  5. Evidence Act 2008 (Vic) s 79(1)

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