There are many cases where a judge has to determine differences between experts. It is helpful for practitioners to know what factors are taken into account when assessing evidence . The Judicial College of Victoria puts all its guidance to judges online for public consumption. It has recently updated its guidance to judges on assessing expert evidence. It has to be remembered that we are not here concerned with the law in England & Wales, however the principles involved are pretty universal.
“7.2 – Assessing expert evidence
In Makita (Australia) Pty Ltd v Sprowles (2001) 52 NSWLR 705, Heydon JA explained that it is only possible to evaluate expert evidence if the expert explains the “essential integers underlying” the opinion and that it is the duty of experts:
to furnish the trier of fact with criteria enabling evaluation of the validity of the expert’s conclusions.
In Alsco Pty Ltd v Mircevic  VSCA 229, Robson AJA examined the jurisprudence on judicial resolution of conflicts between experts. He noted that judges are not to resolve such conflicts by purporting to develop their own expertise and substitute their own opinion for that of the experts. Instead, the judge will find a basis for preferring the evidence of one expert (or group of experts) over another, such as:
which opinion best aligns with the primary facts the judge finds;
which opinion appears to be the most credible;
a comparison of the qualifications, expertise or experience of the competing experts;
which expert appeared to be the most objective;
the responses of the experts under cross-examination, or whether the expert was not tested under cross-examination (Alsco Pty Ltd v Mircevic  VSCA 229, -).
In Alsco Pty Ltd v Mircevic  VSCA 229, Judge Kings had found a causal relationship between the plaintiff’s employment and the development of a cervical dystonia. In that case, the evidence established that the majority of cervical dystonia are idiopathic (without an identified cause) and there was conflicting expert evidence on whether a causal relationship existed for this plaintiff. The judge resolved the conflict based on the quality of the evidence when tested in court, the specialisation of the practitioners and the length of time the practitioner treated the plaintiff. This approach was upheld on appeal.
It is not sufficient for a judge to refer to the existence of competing medical opinions and then to prefer one position over the other. The obligation to give reasons (see chapter 10) requires judges to refer to the contradictory evidence and explain why the judge prefers one view. This obligation is especially significant where the disagreement between the experts relates to questions of degree, rather than offering competing views on the cause of the injury or the prognosis of the injury (see Mutual Cleaning and Maintenance Pty Ltd v Stamboulakis (2007) 15 VR 649, -)”