While expert witnesses are traditionally retained to provide their opinion on an issue in a case, parties sometimes retain experts for a more tactical purpose – to critique the opposing expert. The nature of the critique may include collateral attacks on the opposing expert, attacks on the opposing expert’s knowledge, and attacks on the procedure the opposing expert employed. In this fifth article in a series on expert evidence, we highlight three decisions in which courts have questioned the utility of an expert witness’ “critique report”, and have ultimately placed little to no weight on it or excluded the evidence altogether.

In the 2015 decision of M v F, 2015 ONCA 277, a child custody dispute, a mother appealed a trial decision granting the father overnight visits with their child on the basis that the judge failed to consider her expert’s report. The Court of Appeal upheld the trial decision, finding that it was reasonable to attribute little weight to the mother’s expert report because the expert was retained for the limited purpose of critiquing the opposing expert. The father’s expert commented on the benefits of overnight visits to the relationship between the father and child, and the mother’s expert focussed only on undermining these benefits without having even met the child.

The Court of Appeal reiterated the existing jurisprudence on “critique evidence”, stating that it is rarely admissible because it does not usually meet the “necessity” criterion in the Mohan test. The parties can critique one another’s experts through cross-examination and argument. As stated by Justice Benotto on behalf of the court, “critique evidence is rarely appropriate. It generally – as here – has little probative value, adds expense and risks elevating the animosity between the parties”.

Lower courts are applying M v F for the principle that critique reports are generally inadmissible. The narrow exception to this rule seems to be when the stakes in the litigation are extremely high, and/or when the critique is focussed on the other expert’s methodology.

For example, in 2016 in Halton Children’s Aid Society v. A.W., 2016 ONCJ 358, a child protection proceeding, the trial judge admitted critique evidence from the mother’s expert witness. The trial judge reasoned that the nature of the critique evidence was distinct from that in M v F. First, the critique evidence was admitted by a parent trying to prevent severance of the parent-child relationship, one of the most serious matters in family law. Second, the subject of the critique was procedure – the scientific testing, methodology and process used by the Crown’s expert in determining parenting capacity.

Although it commonly arises in the family law context, the restricted use of critique evidence is relevant elsewhere. In Christoforou v. John Grant Haulage Ltd., 2016 CHRT 14, the Applicant brought a complaint pursuant to sections 7 and 10 of the Canadian Human Rights Act that the Respondent employer discriminated against him based on his age and disability by terminating his employment in response to his request to work reduced hours. Prior to the commencement of the Tribunal hearing, the Applicant sought an order excluding the Respondent’s expert on the basis that the purpose of the expert’s evidence was to discredit the treating physician by criticizing her diagnosis of the Applicant’s disability. The Tribunal held that the treating physician would be cross-examined on the very same points raised by the expert and the Tribunal itself would make findings on whether the diagnosis was credible, ultimately determining the weight to give to the opinion. Thus, without offering anything more, such as scientific or technical information, the expert’s evidence was not necessary.

Civil litigators should carefully consider the utility of hiring an expert for the sole purpose of critiquing the opposing party’s expert. Where the expert is stepping into the role of counsel by effectively doing what a cross-examination should do, or the role of the trier of fact by offering an opinion regarding the credibility or reliability of the opposing party’s expert, the resulting report will not likely be admissible, except in rare circumstances when the stakes in the litigation are extremely high, such as in child protection proceedings, and/or when the report only critiques the other expert’s methodology.