Heydon JA (formerly known as his Honour) provided a significant statement in the Makita (Australia) Pty Ltd v Sprowles case regarding the evidentiary requirements for introducing expert evidence in litigation proceedings in New South Wales. This statement serves as a key guideline for litigants.

In essence, for expert opinion evidence to be admissible, several requirements must be met. Firstly, there must be a recognized field of specialized knowledge. Secondly, the expert witness must demonstrate their expertise in a specific aspect of that field through training, study, or experience. The opinion presented must be primarily based on the expert's specialized knowledge. If the opinion relies on facts observed by the expert, those facts must be clearly identified and proven by the expert. If the opinion is based on assumed or accepted facts, those facts must be identified and proven through alternative means. It is crucial to establish that the facts forming the basis of the opinion are reliable and relevant. Furthermore, the expert must provide an explanation of how their specialized knowledge applies to the assumed or observed facts, demonstrating the intellectual or scientific foundation of their conclusions. Failure to explicitly address these criteria may render the evidence inadmissible or diminish its weight. Attempting to clarify the basis of the opinion may uncover that it relies not on specialized expert knowledge but on a mixture of speculation, inference, personal and second-hand views regarding the credibility of the complainant, and a reasoning process that extends beyond the realm of expertise (as described by Gleeson CJ in HG v The Queen [1999] 197 CLR 414]).