By Sarah D. Pinsonnault
Expert witnesses have a duty to the court to give fair, objective and non-partisan opinion evidence. In Québec, the current version of the Code of Civil Procedure, RLRQ, c. C-25 states, under article 418, that the expert must “perform his duties faithfully and impartially”. The new Code of Civil Procedure, RLRQ, c. C-25.01 provides, at article 22, that experts “must fulfill their mission objectively, impartially and thoroughly” and that this “mission overrides the parties' interests”. In White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, the Supreme Court of Canada ruled that the question of an expert witness’ potential bias (i.e. the appearance of favouring one party’s position over another) is not relevant to the question of whether he will be unable or unwilling to fulfill his primary duty to the court.
With respect to the expert’s duty to the court, Justice Cromwell wrote on behalf of a unanimous court:
“ Underlying the various formulations of the duty are three related concepts: impartiality, independence and absence of bias. The expert’s opinion must be impartial in the sense that it reflects an objective assessment of the questions at hand. It must be independent in the sense that it is the product of the expert’s independent judgment, uninfluenced by who has retained him or her or the outcome of the litigation. It must be unbiased in the sense that it does not unfairly favour one party’s position over another. The acid test is whether the expert’s opinion would not change regardless of which party retained him or her: P. Michell and R. Mandhane, “The Uncertain Duty of the Expert Witness” (2005), 42 Alta. L. Rev. 635, at pp. 638-39. These concepts, of course, must be applied to the realities of adversary litigation. Experts are generally retained, instructed and paid by one of the adversaries. These facts alone do not undermine the expert’s independence, impartiality and freedom from bias.”(emphasis added)
On the question of admissibility of an expert’s evidence, he concluded that “the dominant view in the Canadian cases” is that an expert’s lack of independence and impartiality should be considered not only in relation to the weight it should be given (if admitted), but also at the admissibility stage of the proceedings.
Regarding the appropriate threshold for admissibility, we are reminded of the four factors established in R. v. Mohan,  2 S.C.R. 9: relevance, necessity, absence of an exclusionary rule and a properly qualified expert. If this initial threshold is met, the second step is the “reliability versus effect factor”, whereby the judge must decide whether expert evidence that meets the preconditions to admissibility is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to the trial process that may flow from the admission of the expert evidence.
Cromwell J. then went on to state that the appropriate threshold for admissibility stems from the expert’s duty to the court, and that his failure to be fair, objective and non-partisan would thus render his evidence inadmissible.
However, he added that exclusion at the threshold stage of the analysis is rather rare and should only occur in very clear cases following a detailed review of the expert’s interest in the litigation or relationship with one of the parties:
“ This threshold requirement is not particularly onerous and it will likely be quite rare that a proposed expert’s evidence would be ruled inadmissible for failing to meet it. The trial judge must determine, having regard to both the particular circumstances of the proposed expert and the substance of the proposed evidence, whether the expert is able and willing to carry out his or her primary duty to the court. For example, it is the nature and extent of the interest or connection with the litigation or a party thereto which matters, not the mere fact of the interest or connection; the existence of some interest or a relationship does not automatically render the evidence of the proposed expert inadmissible. In most cases, a mere employment relationship with the party calling the evidence will be insufficient to do so. On the other hand, a direct financial interest in the outcome of the litigation will be of more concern. The same can be said in the case of a very close familial relationship with one of the parties or situations in which the proposed expert will probably incur professional liability if his or her opinion is not accepted by the court. Similarly, an expert who, in his or her proposed evidence or otherwise, assumes the role of an advocate for a party is clearly unwilling and/or unable to carry out the primary duty to the court. I emphasize that exclusion at the threshold stage of the analysis should occur only in very clear cases in which the proposed expert is unable or unwilling to provide the court with fair, objective and non-partisan evidence. Anything less than clear unwillingness or inability to do so should not lead to exclusion, but be taken into account in the overall weighing of costs and benefits of receiving the evidence.
 As discussed in the English case law, the decision as to whether an expert should be permitted to give evidence despite having an interest or connection with the litigation is a matter of fact and degree. The concept of apparent bias is not relevant to the question of whether or not an expert witness will be unable or unwilling to fulfill its primary duty to the court. When looking at an expert’s interest or relationship with a party, the question is not whether a reasonable observer would think that the expert is not independent. The question is whether the relationship or interest results in the expert being unable or unwilling to carry out his or her primary duty to the court to provide fair, non-partisan and objective assistance.” (emphasis added)
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