The Evidence Act 1995 (NSW) provides that evidence of an opinion is inadmissible (s.76(1)) except where the witness providing the opinion has specialised knowledge based on his or her training, study, or experience and the opinion provided is wholly or substantially based on that knowledge (s.79). In other words, opinion evidence is admissible if a Court is satisfied that the witness is an expert in a particular field.
Parties to litigation instruct experts to provide evidence in support of their case. This evidence can make or break a party’s case and briefing an expert will attract additional costs. It is therefore crucial to ensure that your expert abides by the principles developed through case law and statute which govern the conduct of an expert witness.
At common law, the requirements of an expert witness are outlined in the decision of Makita (Australia) Pty Ltd v Sprowles  NSWCA 305. The common law requirements are reproduced in the expert witness code of conduct under Schedule 7 of the Uniform Civil Procedure Rules 2005 (UCPR). Failure to comply with the requirements will either render an expert’s evidence inadmissible or reduce its weight.
In summary, an expert’s evidence must explain how the field of specialised knowledge in which the witness is expert by reason of training, study, or experience, and on which the opinion is wholly or substantially based, applies to the facts assumed or observed so as to produce the opinion propounded (Makita ).
An expert must disclosure and explain to the Court all documents and material consulted. Calculations, examinations, tests, and investigations conducted must also be explained to the Court and detailed in the expert’s report. The disclosure must enable a reader to arrive at a proper understanding of the approach taken by the expert. It is not enough to simply refer or annex a document without proper explanation as to how it influenced the expert’s findings. Failure to adequately explain material consulted and examinations conducted will render the evidence inadmissible. For example, in Maudsley v The Proprietors of Strata Plan Number 39794  NSWCA 244, the plaintiff’s expert failed to adequately explain the meaning of the results obtained and the Court of Appeal upheld the decision in the lower Court where it was held that the expert’s report and its conclusions carried no conviction.
Like a legal practitioner’s duty to assist the Court in the doing of justice according to law, an expert witness is required to assist the court impartially on matters relevant to his or her area of expertise; an expert is not an advocate for a party.
For a complete list of and commentary on the requirements of an expert witness see: Makita (Australia) Pty Ltd v Sprowles  NSWCA 305 and the expert code of conduct under the UCPR.
Written by Malik Anne.