Cross-examination of an expert witness is a common technique used by legal counsel to discredit the testimony provided by an expert witness. Expert witnesses may be cross-examined on a variety of issues such as their experience in their chosen field, the methods used to reach their conclusions or any prior inconsistent statements made by the expert. One area of cross-examination recently considered by Canadian courts is whether expert witnesses can be cross-examined on adverse findings of credibility which were made in prior judicial hearings. Set out below is a discussion of the development of this area of law in Canada and the US and a consideration of the cross-examination culture in Australia in relation to expert witnesses.
Bruff-Murphy v Gunawardena
In the Canadian case of Bruff-Murphy v. Gunawardena (Bruff-Murphy), an expert witness engaged by the defence had a chequered history with respect to the provision of expert testimony. On three occasions prior to the hearing of the Bruff-Murphy case, the expert had been subject to adverse judicial determinations where his evidence was rejected on the basis of partiality. In essence, the expert had been found to act as an advocate for the defence rather than as an impartial witness.
Based on the decision in R. v. Ghorvei, the court declined to allow cross-examination on this issue. In R. v. Ghorvei, the court on the issue of cross-examination of an expert witness in relation to prior adverse judicial determinations found that:
“it is not proper to cross-examine a witness on the fact that his or her testimony has been rejected or disbelieved in a prior case…. The triers of fact who would witness this cross-examination would not be able to assess the value of that opinion and the effect, if any, on the witness’s credibility without also being provided with the factual foundation for the opinion.”
It was held that a prior adverse judicial determination against an expert witness was “in essence, no more than an opinion on the credibility of unrelated testimony given by this witness in the context of another case.”
Further Canadian cases have commented on this rule and have provided insight into the policy rationale behind the ruling. These cases have noted that using the fact that an expert has been the subject of an adverse judicial determination in a former case as evidence in a different case presents significant problems. The trier of fact in the second case does not have recourse to the reasoning behind the trier of fact’s decision to disallow the evidence in the first case.
Canadian commentary on this line of authority has questioned this rationale on the grounds that a prior adverse determination in relation to an expert witness should be a “red flag” to the trier of fact in the current case on the issue of whether or not the witness is impartial, regardless of whether or not the reasons behind the determination are given. Additionally, comments have been made as to the gravity of the prior adverse determinations in R. v. Ghorvei, with the expert, in that case, having been subject to only one prior determination. Commentators on the issue have questioned whether the reasoning, in this case, should be extended to cases where the witness in question has a history of adverse determinations in relation to their expert testimony.
The New York case of People v Wilson set out the approach that U.S. Federal Courts have taken in relation to questioning expert witnesses on prior judicial determinations. The court held that a defendant does not have an automatic entitlement to cross-examine an expert witness about a prior judicial determination of a lack of credibility. However, it did find that prior judicial rulings concerning the credibility of a witness could be probative of the witness’ credibility in a different case. The court drew attention to the decision in United States v Cedeno where the court set out various factors which should be used to determine whether a prior judicial determination of incredibility could form the basis of a line of questioning in cross-examination at a different trial. These factors included:
- Whether statements which were the subject of an adverse determination were made under oath in a judicial proceeding or made in a less formal context;
- The amount of time which has elapsed since the determination; and
- The motive for the untruthful statements told and whether an explanation was provided.
Expert witness crosses-examination in Australia
The New South Wales Bar Association provides guidance on the issue of cross-examination of expert witnesses, noting that the following may be questioned in relation to admissibility:
- The area of expertise claimed by the expert is not a sufficiently recognised field of specialist knowledge or is common knowledge and thus not suitable for the provision of expert evidence.
- The witness has insufficient training, experience, or qualifications necessary to be classified as a witness.
As to the weight of evidence given by an expert, the following issues may arise on cross-examination:
- The facts, assumptions, methods, and reasoning used by the expert;
- The qualifications or experience of the expert;
- A comparison of the expert’s opinion and that of other experts; and
Cross-examination based on prior judicial determinations is not contemplated by the New South Wales Bar Association.
A review of Australian case law does not produce any analogous cases to Bruff-Murphy, and it thus remains to be seen whether or not Australian courts would allow this line of cross-examination. Should Australian courts follow Canadian judicial authority, it appears almost certain that evidence of prior adverse judicial determinations would not be admitted into evidence. However, should Australian courts follow the US approach, the possibility of such cross-examination would arise, though the right this would not be automatic.
 2016 ONSC 7
 2016 ONSC 7
 For example, Wasylyshen v. Alberta (Law Enforcement Review Board), 2008 CarswellAlta 2011, 2008 ABCA 432,  A.W.L.D. 1962, 174 A.C.W.S. (3d) 315, 3 Alta. L.R. (5th) 223, 442 W.A.C. 127, 446 A.R. 127, 85 Admin. L
 Alan Shanoff, Social Justice: Expert Witnesses Cross Examination Conundrum (Law Times, 6 June 2016).
 2016 NY Slip Op 30734
 644 F.3d 79, 83 (2nd Cir 2011)