There is an ongoing debate about whether judges who are after all themselves lawyers, need expert evidence about what competent lawyers tend to do in any given situation. But it is clear that there are occasions when expert evidence of good professional practice is admissible in some solicitors’ negligence cases. And certainly, expert evidence is an important feature of professional negligence cases against other professionals. Experts are not supposed to give evidence of the ultimate issue, though that is a more complicated proposition, once you start analysing it, than it sounds. Generally speaking though, an expert should say ‘in this situation, a competent professional would generally engage in a range of responses, from X to Y’, and should never say ‘I think the defendant was negligent in failing to do Z’. With this kind of expert evidence, though, it is difficult to know when one proposition is just a rewording of another. The limits of what the expert can properly say are, to my mind at least, somewhat cloudy. In a recent decision in a stockbroker’s negligence case, Eric Preston Pty Ltd v Euroz Securities Limited  FCA 213, Justice Siopsis reiterates and summarises the relevant principles articulated in Australian Securities and Investments Commission v Vines  NSWSC 1095; (2003) 48 ACSR 291, as follows:
‘First, a professional expert may give “evidence about the content of general practices of professionals in his or her field, or to put it another way, evidence about what professionals generally do in stated circumstances”. Secondly, a professional may “go beyond evidence of the content of general practices, by expressing an opinion about the practice of competent and careful professionals in specified circumstances which are recurring or typical”. Thirdly, expert evidence is admissible as to what “a reasonably competent and careful [professional] would or should do in precisely specified circumstances”. This would include evidence of what “in stated circumstances which are out of the ordinary and not amenable to observations about a developed practice, a competent and careful professional would be expected to do”. Austin J referred to the case of Rabelais Pty Ltd v Cameron  ANZ Conv R 457 (Rabelais) as authority in support of this proposition. Fourthly, evidence of what the expert would do himself or herself in stated circumstances is inadmissible. Fifthly, when considering objections to expert witnesses in limine on the grounds that the opinion is not based wholly or substantially based on the expert’s specialised knowledge, the test is whether the court is satisfied on a balance of probabilities that the opinion is based wholly or substantially on specialist knowledge.’
The other interesting thing about the decision is the Court’s willingness to deal with objections to expert evidence in limine. On this question see also Justice Hansen’s decision in Rod Investments (Vic) Pty Ltd v Abeyratne  VSC 40.