It is safe to say that pretty much everyone working in the forensic sciences has heard of the Daubert ruling or, more specifically, Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).1 It was a pivotal ruling that, together with two subsequent rulings General Electric Co. v Joiner, 522 U.S. 136 (1997)2 and Kumho Tire Co., Ltd. v Carmichael, 526 U.S. 137 (1999),3 has greatly affected many legal jurisdictions in the United States. And, as is often the case, whatever happens in the USA tends to have influence elsewhere.

R. v. Mohan — Canada's Daubert

Shortly after that, in Canada, there was a key Supreme Court ruling that addressed admissibility of forensic expertise — R. v. Mohan, [1994] 2 S.C.R. 9.4

That ruling laid out the test for the admissibility of ‘novel’ expert evidence (see Mohan, page 4) in Canada.

Subsequently, the factors explained in that ruling have been applied, just as those in Daubert were, to many types of traditional forensic science evidence. It is, perhaps, rather ironic that rulings intended to liberalize the admission of new (and potentially) helpful evidence would lead to challenges of all forms and types of evidence.

In Mohan, Justice Sopinka outlined four broad elements that a trial judge should consider when deciding whether or not to admit the evidence of a given ‘expert’. The court wrote, in part:

Admission of expert evidence depends on the application of the following criteria: (a) relevance; (b) necessity in assisting the trier of fact; (c) the absence of any exclusionary rule; and (d) a properly qualified expert. Relevance is a threshold requirement to be decided by the judge as a question of law. Logically relevant evidence may be excluded if its probative value is overborne by its prejudicial effect, if the time required is not commensurate with its value or if it can influence the trier of fact out of proportion to its reliability. The reliability versus effect factor has special significance in assessing the admissibility of expert evidence. Expert evidence should not be admitted where there is a danger that it will be misused or will distort the fact-finding process, or will confuse the jury.

Before looking at the Mohan criteria in detail, consider that this ruling has been cited over 3,500 times.5 So there is no doubt it has been very influential in the Canadian justice system. Included in those citing rulings were R. v. J.-L.J., 2000 SCC 51, [2000] 2 SCR 600,6 R. v. Trochym, 2007 SCC 6, [2007] 1 SCR 239,7 and R. v. Abbey, 2009 ONCA 624 (CanLII).8 These cases are of particular interest insofar as they expand upon and clarify some facets of the Mohan ruling and each has been influential in its own right.

The four criteria laid out by Justice Sopinka for the admission of expert evidence were simply:

  • Relevance,
  • Necessity in assisting the trier of fact,
  • Absence of exclusionary rule, and
  • Properly qualified expert.

Let’s look briefly at each of these.9 These four factors were discussed in the context of the trial judge serving as ‘gatekeeper’ as they determine whether or not a witness should be admitted and allowed to provide expert testimony. Further, as the above quote indicates, the judge must also perform a proper assessment, a ‘cost-benefit’ analysis, that balances “reliability versus effect factor”.


Relevance is a threshold requirement for the admission of expert evidence as with all other evidence. Relevance is a matter to be decided by a judge as question of law. Although prima facie admissible if so related to a fact in issue that it tends to establish it, that does not end the inquiry. This merely determines the logical relevance of the evidence. Other considerations enter into the decision as to admissibility.

The Court was clearly concerned here that expert evidence might be misused, mis-represented or mis-interpreted such that the evidence could “distort the fact-finding process”. Justice Sopinka was clear on this when he wrote “Dressed up in scientific language which the jury does not easily understand and submitted through a witness of impressive antecedents, this evidence is apt to be accepted by the jury as being virtually infallible and as having more weight than it deserves.”

Necessity: Quoting Dickson, J in R. v. Abbey (1982), Justice Sopinka wrote:

What is required is that the opinion be necessary in the sense that it provide information “which is likely to be outside the experience and knowledge of a judge or jury”.

Further, “the evidence must be necessary to enable the trier of fact to appreciate the matters in issue due to their technical nature.” Such thoughts align with many similar rulings but Justice Sopinka again reiterated that ‘necessity’ was be “assessed in light of its potential to distort the fact-finding process.” Beyond its potential to “overwhelm the jury and distract them from their task” such evidence also runs the risk of usurping the function of the trier of fact. As Justice Sopinka put it “There is also a concern inherent in the application of this criterion that experts not be permitted to usurp the functions of the trier of fact.”

Absence of Exclusionary Rule: Regardless of any issues that may arise under the other three criteria, Justice Sopinka noted that relevant and necessary expert evidence given by a qualified person may still be non-admissible if it runs afoul of some exclusionary rule. He wrote:

Compliance with criteria (a), (b) and (d) will not ensure the admissibility of expert evidence if it falls afoul of an exclusionary rule of evidence separate and apart from the opinion rule itself.

Properly Qualified Expert: Surprisingly little was written on this point by Justice Sopinka. Perhaps because it has been addressed in other rulings. He put it simply:

Finally the evidence must be given by a witness who is shown to have acquired special or peculiar knowledge through study or experience in respect of the matters on which he or she undertakes to testify.

In a way the idea of ‘proper qualification’ may seem a bit redundant with the whole idea of admissibility, in general. After all, isn’t the issue of admissibility of the evidence tied to qualifications of the person testifying? Yes, it is to some degree, but strictly speaking, it is not. Under Mohan, they are linked expressly because this was included as one of the criteria.

The two are, in fact, separate issues. One can consider the proposed evidence in general terms leaving the competency of the expert entirely out of the equation. This was the approach taken in Daubert. Alternatively, one may consider the competency of the expert without concern for the science in general. Mind you, the latter makes little sense — unless a science (or method) is generally valid, how could a practitioner be qualified to apply it in any meaningful manner? Lastly, one may consider both of these together and this is the approach taken in Mohan by inclusion of this ‘requirement’.

What makes a witness “properly qualified”? First, the witness must be “shown to have acquired special or peculiar knowledge through study or experience in respect of the matters on which he or she undertakes to testify”. Obviously, as noted above under ‘necessity’, such knowledge must clearly be “beyond the ken of the average lay person”. There is no pre-set list of the things that can be used to show the person has ‘acquired special or peculiar knowledge through study or experience’. At the same time, a few things should be obvious. For example, training, experience, ongoing learning and development, and knowledge of (and how to use) reliable and accurate examination techniques.

The overall review procedure is outlined in the following paragraph:

In summary, therefore, it appears from the foregoing that expert evidence which advances a novel scientific theory or technique is subjected to special scrutiny to determine whether it meets a basic threshold of reliability and whether it is essential in the sense that the trier of fact will be unable to come to a satisfactory conclusion without the assistance of the expert. The closer the evidence approaches an opinion on an ultimate issue, the stricter the application of this principle.

Now, let’s consider the other cases mentioned above. First, R. v. J.-L.J. was, to my knowledge, the first Canadian ruling to cite Daubert directly thus introducing the latter formally into our legal system. R. v. J.-L.J. again dealt with ‘novel’ scientific evidence10 and the issue on appeal was whether the trial judge had fulfilled his gatekeeper function.11

Justice Binnie referenced Daubert directly in his discussion of “general acceptance” and the move, both in Canada and the USA, towards a more complete assessment of “novel” forms of scientific evidence:

Mohan kept the door open to novel science, rejecting the “general acceptance” test formulated in the United States in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), and moving in parallel with its replacement, the “reliable foundation” test more recently laid down by the U.S. Supreme Court in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). While Daubert must be read in light of the specific text of the Federal Rules of Evidence, which differs from our own procedures, the U.S. Supreme Court did list a number of factors that could be helpful in evaluating the soundness of novel science…

The court then listed the Daubert (non-inclusive, non-mandatory) criteria:

  1. whether the theory or technique can be and has been tested
  2. whether the theory or technique has been subjected to peer review and publication
  3. the known or potential rate of error or the existence of standards
  4. whether the theory or technique used has been generally accepted

But the court did not take this further in their analysis.

The court in R. v. Trochym, on the other hand, drew upon J.-L.J. and applied those criteria to the case at hand (interestingly, leaving out the issue of the existence of standards). In addition to formerly applying the criteria, the judgment discusses many other issues of interest. For one, the court tried to emphasize the potential need to ‘screen’ all scientific techniques in a similar manner regardless of previous acceptance. Madame Justice Deschamps J for the majority wrote:

Not all scientific evidence, or evidence that results from the use of a scientific technique, must be screened before being introduced into evidence. In some cases, the science in question is so well established that judges can rely on the fact that the admissibility of evidence based on it has been clearly recognized by the courts in the past. Other cases may not be so clear. Like the legal community, the scientific community continues to challenge and improve upon its existing base of knowledge. As a result, the admissibility of scientific evidence is not frozen in time.

It is hard to argue with this point. The court clearly left trial judges with the option of admitting evidence based on precedence, but it is also clear they felt all forms of evidence could potentially be subject to this type of review.

This contrasts a bit to the dissenting position espoused by Justice Bastarache writing in the minority, “The approach to hypnotically refreshed evidence as novel science raises concerns not only with respect to the views on the admissibility of such evidence, but also with respect to the implications for the admissibility of scientific evidence in future cases.” There were four elements to the dissenting opinion.

The first comments on the concept of ‘novel science’ and whether previously admitted types of evidence need to be reviewed in this manner.

First, characterizing hypnosis as novel science ignores the fact that the technique has been used in Canada for almost 30 years, and has been employed in Canadian criminal investigations to assist in memory retrieval for a similar length of time. While the use of forensic hypnosis has not been assessed under the framework to determine admissibility of novel scientific evidence, this does not mean that evidence derived from this technique has been admitted into trials without sufficient scrutiny of its reliability. Very few Canadian courts have admitted hypnosis evidence without a voir dire as to its admissibility.

The second relates to the scope of any admissibility ‘test’ and the need to be ‘flexible and nonexclusive’.

Second, the test for assessing the reliability of scientific evidence is not new law requiring that scientific methods, previously accepted as legitimate by our courts, must now be resubmitted for scrutiny. Rather, the test emphasizes the need for courts to give special scrutiny to novel science or the new application of a recognized science, through a case-by-case evaluation, in light of the changing nature of our scientific knowledge. The test was not intended to set down a rigid formula where the results must be proved beyond a reasonable doubt before scientific evidence can be admitted. The factors adopted were designed to be flexible and nonexclusive.

The third touches on the idea of consensus, aka “general acceptance”, as a requirement for admissibility.

Third, the test was not meant to require a standard of total consensus by members of the scientific community. Total unanimity, which is a standard akin to the “general acceptance” test recently rejected by this Court, is impossible to obtain and therefore completely unrealistic to expect. To require such a high standard of reliability will result in the exclusion of far too much relevant and probative evidence.

The last point addressed the need for case-by-case review and assessment.

Finally, it is especially problematic to adopt a general exclusionary rule towards hypnosis evidence by relying almost exclusively on the position of experts discussed in American cases cited. To rely on expert evidence heard in other cases deprives a party of the right to present contrary evidence or to cross-examine the experts who maintain such a position. A court should never take judicial notice of expert evidence.

Overall, between the majority and minority views of the Justices, I consider the Trochym ruling to be essential reading for all forensic practitioners.

It is also interesting to consider how Mohan compares to Daubert in rather more practical terms. Conceptually and philosophically there is a lot of cross-over between the two rulings which is not surprising as they relate to the same issue, admissibility of expert evidence. Certainly the terminology differs, which may reflect the legal heritage and context more than anything else, but the intent seems to be the same.

Beyond this and speaking in purely practical terms, Daubert challenges in the USA are usually (always?) a pre-trial motion to exclude. As a result, the examiner and their counsel have an opportunity to prepare a proper, often very extensive and thorough, response. When this has been achieved, the results have generally been positive for the forensic examiner but, as per human nature, it isn’t always handled well. In those instances much less positive rulings have been the result.

In Canada, on the other hand, it is less common to see a pre-trial motion to exclude. Not that it will never happen but it is much more likely for this to come up in the course of normal court proceedings where a witness has been called by one side and the other side challenges the admissibility of their evidence. As a result, there is little or no warning or special preparation possible. Each and every witness must be prepared to provide full and complete information to the court thereby allowing the sitting judge to reach a proper decision. This generally happens in the course of a voir dire for admissibility of the evidence.

The Canadian approach is both good and bad. It’s good because a poorly qualified individual is, in my opinion, less likely to be accepted by the courts based on the belief that they won’t be capable of providing ‘adequate’ information. It is bad if a properly qualified examiner is unable, for any reason, to provide ‘adequate’ information. It can be legitimately argued that the latter should not happen if the examiner is truly qualified but, in reality, it can and it does happen. Perhaps more important, it is also bad because this approach expects every trial judge to be fully qualified to assess scientific evidence, regardless of the type of evidence.

Perhaps that’s simply a price that must be paid. In my personal opinion, Canadian (and American) courts still tend to be overly lenient about admitting ‘experts’ brought before them.

All in all, the issues raised under Daubert and Mohan are similar. From the perspective of an examiner hoping to be qualified and accepted in a court of law as an expert witness the preparation should be essentially the same regardless of the standard being applied by the court.


  1. Read the Daubert v. Merrell Dow Pharmaceuticals ruling here.
  2. Read General Electric Co. v Joiner ruling here.
  3. Read the Kumho Tire Co., Ltd. v Carmichael ruling here.
  4. Read the R. v. Mohan ruling here.
  5. UPDATED:  Statistics from CanLII, as of 2024-Jan-19)
  6. Read R. v. J.-L.J. ruling here.
  7. Read R. v. Trochym ruling here.
  8. Read R. v. Abbey ruling here.
  9. This is obviously not a legal analysis. It us just my perspective as a forensic examiner.
  10. The witness in the case was a psychiatrist who pioneered (in Canada) the use of a “penile plethysmograph”; something previously used as a therapeutic tool but now being proposed for forensic work.
  11. Following the voir dire the trial judge had excluded the expert evidence because he was not persuaded that the Mohan requirements had been met.

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