Qualification of your expert vs. reliability of the expert opinion

By Chris Wullum

As discussed in an earlier article on Expert Evidence, Its Threshold Admissibility and the Court’s Gatekeeper Role, the Court has a two-step process in determining whether expert evidence meets the criteria for admissibility in a case.  This two-step process starts with an analysis of the four factors from R. v. Mohan, [1994] 2 S.C.R. 9, which sets out the threshold factors for admissibility:

  1. The evidence is relevant to some issue in the case;
  2. The evidence is necessary to assist the trier of fact;
  3. The evidence does not contravene an exclusionary rule; and
  4. The witness is a properly qualified expert.

The second stage of the process is an exercise of the judge’s “gatekeeper” role to perform a discretionary cost-benefit analysis as to whether the proposed evidence is sufficiently beneficial to the trial process when assessed against any potential harm from its admission (the probative value vs. its prejudicial effect). 

This two-step analysis was confirmed most recently in R. v. Abbey (No 2), 2017 ONCA 640 where the Ontario Court of Appeal neatly summarized the process at para. 48 as:

“Expert evidence is admissible when:

(1) It meets the threshold requirements of admissibility, which are:

a.   The evidence must be logically relevant;

b.   The evidence must be necessary to assist the trier of fact;

c.   The evidence must not be subject to any other exclusionary rule;

d.   The expert must be properly qualified, which includes the requirement that the expert be willing and able to fulfil the expert’s duty to the court to provide evidence that is:

                                      i.       Impartial,

                                    ii.       Independent, and

                                    iii.       Unbiased.

e.   For opinions based on novel or contested science or science used for a novel purpose, the underlying science must be reliable for that purpose,


(2) The trial judge, in a gatekeeper role, determines that the benefits of admitting the evidence outweigh its potential risks, considering such factors as:

a.   Legal relevance,

b.   Necessity,

c.   Reliability, and

d.   Absence of bias.”

Recently, the Nova Scotia Court of Appeal wrestled with clarifying the issue of when and how a trial judge should consider the issues of qualifying an expert as well as the reliability of the expert’s opinion.  In Nova Scotia (Community Services) v. J.M., 2018 NSCA 71 the Court reviewed a trial decision in a child protection case where the judge conflated the qualifications of a medical biochemist and the reliability of the lab’s testing process and results.  The trial judge stated in ruling the doctor’s evidence inadmissible: “Dr. Nassar’s qualifications must therefore be assessed in conjunction with the toxicology lab that he directs and from which the toxicology results were garnered.”

The Court of Appeal however ruled that this approach was in error and was not in keeping with the two-step process set out by the Supreme Court.  The Court stated that the qualifications of the expert, and the reliability of the expert’s evidence are two separate legal questions.  The trial judge ought to have first assessed the qualifications of the expert.  This includes the expert being impartial, independent and unbiased.  In Nova Scotia v. J.M., the expert Dr. Nassar was found to have strong expert credentials and in his testimony he confirmed his understanding of his obligations of fairness, objectivity and non-partisanship.  Therefore, the expert should have been considered qualified to provide the opinion.

The Court of Appeal went on to say that the issue of the reliability of the expert evidence in the case was best addressed at the second gatekeeper stage of the two-step analysis.  At this stage, the probative value of the evidence, in terms of relevance, reliability, and necessity, can be weighed against the cost it would have to the fairness of the trial in terms of time consumption, confusion, and prejudicial effects.  The concerns related to the lab’s lack of forensic accreditation, and Dr. Nassar’s role as its director was most properly addressed in the second step gate-keeper stage.  Ultimately, the Court of Appeal decided that the cost-benefit analysis would have favoured the admission of the expert testimony.

This case is important in the series of expert evidence decisions related to the two-step admissibility analysis to clarify at what stage each of these issues might best be considered by the trial judge.  The decision suggests that the trial judge should not consider reliability of the opinion in determining whether the expert is properly qualified or not, and that reliability is best addressed through the second stage gatekeeper role.