Legal Requirements for Qualified Expert Evidence
A trial judge must determine on a voir dire whether the individual is qualified as an expert, and if so, what the "nature and scope of the proposed expert evidence" will be. The qualification process is one of delineating the boundaries of the evidence and the language used. 
The judge cannot permit the expert to give an opinion on common matters or matters that the expert has no special skills, knowledge, or training.
The qualification involves two phases. First, the adducing party "must establish the threshold requirements of admissibility" under the Mohan test. Second, the judge must exercise discretion as a gatekeeper and balance the "potential risks and benefits of admitting the evidence".
The primary purpose of the limiting of opinion evidence is to avoid usurping the trier-of-fact's authority to decision decide a case, and devolve the trial process devolving into a "trial by expert".
There is a danger that an improperly qualified expert will give evidence that will be misused and distort the fact-finding process. This is made worse given that counsel is not an expert in the field and may not be able to critically evaluate the claims through cross-examination.
A secondary purpose is to ensure that time and money are not wasted needlessly.
- Court's Ongoing Obligation to Evaluate Admissibility
Courts must be "vigilant in monitoring and enforcing the proper scope of expert evidence" given the impact that they have on a trial including the risk of "usurping the role of the trier-of-fact. This supervision must occur "throughout the expert's testimony" and not simply at the voir dire.
- R v Preeper and Doyle, 1888 CanLII 56 (SCC), (1888), 15 SCR 401
R v Abbey, 2009 ONCA 624 (CanLII), per Doherty JA
White Burgess Langille Inman v Abbott and Haliburton Co, 2015 SCC 23 (CanLII), per Cromwell J, at paras 22 to 24
R v AK, 1999 CanLII 3793 (ONCA), 137 CCC (3d) 225, per Charron JA
White Burgess, supra, at para 23
White Burgess, ibid., at para 24
- White Burgess, supra, at para 18 ("The point is to preserve trial by judge and jury, not devolve to trial by expert")
- R v Mohan, 1994 CanLII 80 (SCC),  2 SCR 9, per Sopinka J ("There is a danger that expert evidence will be misused and will distort the fact-finding process. 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.")
White Burgess, supra, at para 18 ("The risk of “attornment to the opinion of the expertˮ is also exacerbated by the fact that expert evidence is resistant to effective cross-examination by counsel who are not experts in that field")
White Burgess, supra, at para 18 ("Another well-known danger associated with the admissibility of expert evidence is that it may lead to an inordinate expenditure of time and money")
Mohan, supra, at p. 21
R v Sekhon, 2014 SCC 15 (CanLII),  1 SCR 272, per Moldaver J, at para 46
R v Shafia, 2016 ONCA 812 (CanLII), per Watt JA, at para 235
Sekhon, ibid., at para 46
Requirements to Qualify an Expert (Mohan Test)
The qualification of an expert requires a two-stage inquiry. First, the evidence must pass the "threshold' requirements of admissibility. Second, the judge must balance the potential risks and benefits of admitting the evidence and decide whether the benefits outweigh the risks.
To qualify a person as an expert, the evidence must meet the Mohan requirements:
- the opinion must be relevant;
- the opinion must be necessary to assist the trier-of-fact to draw the correct inference;
- the absence of any other exclusionary rule;
- the required qualifications of the proposed expert.
The Mohan test assumes that the area of science is not novel. Where the subject matter is novel, contested, or being used for a novel purpose, there is an additional requirement that the party adducing the evidence show that subject matter is reliable "for that purpose".
- White/Abbey Approach to Mohan
The preferred analytical approach to the Mohan test is to perform a two stage analysis.
- First Stage – Threshold Requirements
The first stage is to consider the "preconditions to admissibility". The evidence must meet the threshold requirements of admissibility, which are:
- The opinion must be logically relevant;
- The opinion must be necessary to assist the trier of fact;
- The opinion must not be subject to any other exclusionary rule;
- 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:
- Independent, and
- For opinions based on novel or contested science or science used for a novel purpose, the underlying science must be reliable for that purpose,
Should the evidence fail the requirements of the first stage, then the evidence is excluded.
- Second Stage – Gatekeeper
The second stage concerns a "gatekeeper inquiry" where the judge "must identify and weigh competing considerations to decide whether, on balance, admissibility of the evidence is favoured." This second stage is effectively a cost-benefit analysis. Factors to consider include:
- Legal relevance,
- Reliability, and
- Absence of bias.
- Case-Specific Analysis
The analysis will be "case-specific" and will be a "function of the other evidence and issues in the case being tried". Absent an error in principle or an unreasonable ruling, the judge's decision on expert evidence requires deference.
- Discretionary Exclusion of Qualified Expert Evidence
Qualified expert evidence can nonetheless be excluded if:
- the evidence would tend to usurp the duty of the trier of fact
- the prejudicial effect outweighs the probative value
- the time required outweighs its probative value
- the cost required outweighs the probative value
- the influence of the evidence outweighs the evidence's reliability.
The proposed expert must have some indicia of scientific knowledge. It cannot be admitted if the witness is giving personal opinions based on their experience or knowledge from "some" literature and interviews.
Expert evidence should be expected to be impartial to be admissible. There must not be any bias or appearance of bias.
- Weight Given to Expert Evidence
Where qualification is consented to by the other counsel, it does not permit the court to assign "weight beyond what the trial judge should otherwise attribute". Weight is attributed by the court based on "reasons given for the expert opinion, the evidence bearing on the basis of the expert opinion and the extent of the expert’s expertise".
Where the expert witness was not properly qualified and still gave evidence, their opinion may still be admissible absent objection from the opposing counsel.
A failure for defence to make objections during trial are not likely obstacles to appeal since it is "foreseeable that defence counsel may fail to object to the testimony at the time the problematic statements are made".
- Expert Evidence Dangers
The courts "must be vigilant in monitoring and enforcing the proper scope of expert evidence" throughout the trial. Simply ruling on the Mohan criteria at the outset is not enough.
Judge's must be cautious that the trial does not devolve into "trial by expert". The trier-of-fact must still be able to make "an effective and critical assessment of the evidence" that is based on "informed judgment" rather than blind faith in the expert's opinion. To avoid this the courts as gatekeepers must watch out for:
- resistance to effective cross-examination by a non-expert counsel;
- potential prejudice created by the expert's reliance on unproven material not subject to cross-examination;
- the admission of "junk" science;
- the risk of distraction from a "contest of experts";
- an inordinate amount of time and money consumed by experts.
- the likelihood of confusing the trier-of-fact;
- the extent of impenetrable jargon.
- the inability of trier-of-fact from making effective and critical assessment of the evidence.
- Appellate Review
Given the "case-specific" nature of the test, the appellate court may intervene where the finding "is clearly unreasonable, contaminated by an error in principle or reflective of a material misapprehension of evidence". The Court must show deferrence to the trial judge's decision.
R v Shafia, 2016 ONCA 812 (CanLII), per Watt JA, at para 226
R v Abbey, 2009 ONCA 624 (CanLII), 246 CCC (3d) 301, per Doherty JA
R v Mohan, 1994 CanLII 80 (SCC), per Sopinka J (9:0)
R v Sekhon, 2014 SCC 15 (CanLII), per Moldaver J (5:2), at para 43
White Burgess Langille Inman v Abbott and Haliburton Co, 2015 SCC 23 (CanLII), per Cromwell J (7:0), at para 23 ("At the first step, the proponent of the evidence must establish the threshold requirements of admissibility. These are the four Mohan factors ... and in addition, in the case of an opinion based on novel or contested science or science used for a novel purpose, the reliability of the underlying science for that purpose: .... Relevance at this threshold stage refers to logical relevance: .. . Evidence that does not meet these threshold requirements should be excluded. Note that I would retain necessity as a threshold requirement: ...")
JLJ, supra, at paras 33, 35 to 36, 47
R v Trochym, 2007 SCC 6 (CanLII),  1 SCR 239, at para 27
R v Abbey, 2009 ONCA 624 (CanLII), 246 CCC (3d) 301, per Doherty JA
R v Abbey, 2017 ONCA 640 (CanLII), per Laskin JA (3:0), at para 48
R v Farnham, 2016 SKCA 111 (CanLII), per Ryan-Froslie JA (3:0), at para 81
Abbey (2009), supra, at para 79
Abbey (2017), supra, at para 48
Abbey (2017), supra, at para 49 ("...if the proposed expert evidence does not meet the threshold requirements for admissibility it is excluded.")
Farnham, supra, at para 81
White, supra, at para 24 ("At the second discretionary gatekeeping step, the judge balances the potential risks and benefits of admitting the evidence in order to decide whether the potential benefits justify the risks. The required balancing exercise has been described in various ways. In Mohan, Sopinka J. spoke of the “reliability versus effect factor” (p. 21), while in J.-L.J., Binnie J. spoke about “relevance, reliability and necessity” being “measured against the counterweights of consumption of time, prejudice and confusion”: para. 47. Doherty J.A. summed it up well in Abbey, stating that the “trial 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”")
Farnham, supra, at para 81
Abbey (2017), supra, at para 48
Shafia, supra, at paras 229, 230 and 234
R v D(D), 2000 SCC 43 (CanLII),  2 SCR 275, per Major J (4:3), at para 12
R v Natsis, 2018 ONCA 425 (CanLII), per Pardu JA, at para 16 ("I begin with the observation that, absent an error in principle or an unreasonable ruling, a trial judge’s decision as to the admissibility of expert evidence is entitled to deference")
R v McManus, 2017 ONCA 188 (CanLII), per van Rensburg JA, at para 68
- DD, ibid.
- R v Bedford, 2000 CanLII 2487 (ON CA), 143 CCC (3d) 311, per Finlayson JA (3:0)
R v Docherty, 2010 ONSC 3628 (CanLII),  OJ No 2460, per Wein J - father of defence counsel writes psych report, found invalid
- R v Strickland, 2013 NLCA 65 (CanLII), per Mercer JA (3:0)
- Strickland, ibid., at para 19
- See Opinion Evidence Outside of Qualification below
- Sekhon, supra, at para 48
- Sekhon, supra, at para 46
White Burgess, supra, at para 18
White Burgess, supra, at para 18
Shafia, supra, at para 233 ("Consumption of time. Prejudice. Confusion. The danger that jurors will be unable to make an effective and critical assessment of the evidence. The complexity of the materials. The impenetrable jargon in which the opinion is clothed. Compromise of the trial process by unduly protracting and complicating proceedings:")
Shafia, supra, at para 230 ("The case-specific nature of the Mohan inquiry has implications for the standard of appellate review. Appellate review is not precluded, as for example, where a finding of admissibility under Mohan is clearly unreasonable, contaminated by an error in principle or reflective of a material misapprehension of evidence.")
Shafia, supra, at para 230
Relevance require the judge to conduct a cost-benefit analysis to determine "whether its value is worth what is costs", which includes weighing the probative value against the prejudicial effect.
The relevance requirement includes both logical relevance (the relationship between the evidence and the fact in issue it is being used to establish) and legal relevance (the probative value). In the first stage of the analysis on threshold reliability, the focus is on logical relevance.
Logical relevance requires that the evidence "have a tendency, as a matter of human experience and logic, to make the existence or non-existence of a fact in issue more or less likely than it would be without the evidence".
It is not legally relevant for a qualified drug expert to say that they have never encountered a blind drug courier in their investigations.
- Anecdotal Evidence from Expert
Anecdotal evidence per se is not inadmissible through the expert, however, depending on the purpose of the expert testimony it may lack legal relevance and necessity.
R v Sekhon, 2014 SCC 15 (CanLII), per Moldaver J, at para 44
R v Mohan, 1994 CanLII 80 (SCC), per Cory J, at pp. 23-24
- R v AK, 1999 CanLII 3793 (ON CA), 137 CCC (3d) 225 (ONCA), per Charron JA
White Burgess Langille Inman v Abbott and Haliburton Co, 2015 SCC 23 (CanLII), per Cromwell J, at para 23
R v Abbey, 2009 ONCA 624 (CanLII), per Doherty JA, at para 82
R v Shafia, 2016 ONCA 812 (CanLII), per Watt JA, at para 227
Abbey, supra, at para 82
R v J-LJ, 2000 SCC 51 (CanLII),  2 SCR 600, per Binnie J (7:0), at para 47
Shafia, supra, at para 227
R v Ma, 1978 CanLII 2438 (ON CA),  OJ No 1425, per Lacourciere JA
R v Boucher, 2000 CanLII 6087 (QC CA), per curiam (3:0)
R v Wilson and Boswell, 2002 CanLII 49653 (ONSC), 166 CCC (3d) 294 (Ont. SCJ), per Kruzick J
R v McLeod,  OJ No 59(*no CanLII links)
Wilson and Boswell, supra
- Sekhon, supra, at para 49
R v Burnett, 2018 ONCA 790 (CanLII), per Watt JA (3:0), at para 58
The necessity requirement is not a strict standard. It is necessary where it furnishes scientific information that is likely to be outside the experience and knowledge of the trier of fact.
The expert evidence must likely outside the ordinary experience and knowledge of the trier of fact. The evidence should not be necessary if “on the proven facts a judge or jury can form their own conclusions without help, then the opinion of [an] expert is unnecessary”.
However, the purpose of this element is to "ensure that the dangers associated with expert evidence are not lightly tolerated" and that mere "helpfulness" is not sufficient.
The subject-matter should be one that a lay person is "unlikely to form a correct judgment about it, if unassisted by persons with special knowledge."
The purpose of the necessity requirement it to protect against the dangers of expert evidence, including the risk of usurping the trier-of-fact, the consumption of time, and consumption of expenses.
- R v B(RH), 1994 CanLII 127 (SCC),  2 SCR 656, per McLachlin J (9:0)
R v Burns, 1994 CanLII 127 (SCC), per McLachlin J (9:0), at paras 24 to 25
R v Mohan, 1994 CanLII 80 (SCC),  2 SCR 9, 89 CCC (3d) 402 (SCC), per Sopinka J (9:0), at pp. 414-415
Mohan, ibid., at p. 23
R v Sekhon, 2014 SCC 15 (CanLII), per Moldaver J (5:2), at para 45
White Burgess, supra, at para 21
Kelliher (Village of) v Smith, 1931 CanLII 1 (SCC),  SCR 672, per Lamont J (3:2)
R v DD, 2000 SCC 43 (CanLII),  2 SCR 275, per Major J (4:3), at para 57
Mohan, supra, at p. 24
Sekhon, supra, at para 45
Properly Qualified Expert
The burden is upon the party calling the witness to prove on a balance of probabilities that they are a "properly qualified expert". The determination of whether a witness is "properly qualified" is based on a "case-specific determination".
Factors to consider in the evaluation of whether the witness is "properly qualified" include:
- The manner in which the witness acquired the special skill and knowledge upon which the application is based;
- The witness' formal education (i.e. degrees or certificates);
- The witness' professional qualifications (i.e. a member of the College of Physicians and Surgeons);
- The witness' membership and participation in professional associations related to his or her proposed evidence;
- Whether the witness has attended additional courses or seminars related to the areas of evidence in dispute;
- The witness' experience in the proposed area(s);
- Whether the witness has taught or written in the proposed area(s);
- Whether, after achieving a level of expertise, the witness has kept up with the literature in the field;
- Whether the witness has previously been qualified to give evidence in the proposed area(s), including the number of times and whether the previous evidence was contested;
- Whether the witness has not been qualified to give evidence in the proposed area(s) and if so, the reason(s) why; and
- Whether previous caselaw or legal texts have identified the contested area as a proper area for expert evidence and if so, who might give the evidence.
A person cannot become a reliable expert by simply conducting "numerous casual conversations with drug users or traffickers". Mere anecdotal evidence cannot be tested or verified.
Experience and Education
An expert does not have to have practical experience.
The essential requirement is that "he should be skilled ... that which he is called upon to give an opinion."
- No Prior Qualification
There is no special rule for "first time" experts that would render them any less eligible for qualification as an expert.
A formal education such as a university degree is not a necessary requirement to be an expert in an area.
- Employment by Police Service
There is no impediment to qualification where the proposed expert is employed by police service.
e.g. R v Morgentaler (No. 2), 1973 CanLII 1462 (QC CQ), 14 CCC (2d) 450 (Que. S.C.), per Hugessen J - gynecologist testified as expert despite having not practiced for 10 years
R v Korski, 2007 MBQB 184 (CanLII), per Beard J, at para 15 citing McWilliams' Canadian Criminal Evidence
R v Plourde, 2017 ABCA 367 (CanLII), per Slatter JA (3:0), at para 5
- R v Dugandzic, 1981 CanLII 3117 (ON CA),  OJ No 1, 57 CCC (2d) 517 (Ont. C.A.), per Lacourcière JA (3:0) - chemistry degree not required to identify a still
R v Godfrey, 1974 ALTASCAD 43 (CanLII), 18 CCC (2d) 90 (Alta. S.C.A.D.), per Allen JA (2:1), at pp. 102-104
R v Marquard, 1993 CanLII 37 (SCC), per McLachlin J (8:1), at p. 243
Plourde, supra, at para 5
Independence, Impartiality and Lack of Bias
Evaluating Novel Fields
Novel sciences must be considered on a case-by-case basis. There are no fixed categories where the requirements for expert evidence have been met. The courts must individually distinguish between new sciences and "junk" sciences. As such, needs "special scrutiny". 
There is no pre-condition that a particular field be "scientifically valid" or otherwise able to be validated by scientific methods.
Novel sciences must only be qualified if it is (1) necessary and (2) reliable
When evaluating scientific evidence, the Court should consider Daubert factors:
- falsifiability of the theory
- peer review and publication of the theory
- known or potential rate of error and the existence of standards controlling the research on which the theory is based and
- general acceptance of the methodology underlying the theory in the scientific community.
- Unsettled Theories
The evidence can still be admissible even if the scientific theory is open to debate or that there are exceptional cases to the theory.
It is not necessary to establish that the field be one that is subject to "peer review".
The fact that an area of scientific theory is open to debate and that exceptional cases fall outside the norm does not preclude the evidence from admissibility.
- Source of Expertise
Expertise "may be acquired through study".
Depending on the subject, it may not be necessary that the expert has a university degree in the subject to be an expert.
The absence of writing or publications will generally go to weight and not admissibility.
An expert is entitled to develop that expertise by observations, by talking to other experts, and by general involvement in the field.
e.g. R v Lavallee, 1990 CanLII 95 (SCC), per Wilson J battered wife syndrome accepted as science
- R v J-LJ, 2000 SCC 51 (CanLII),  2 SCR 600, per Binnie J (7:0)
R v Shafia, 2016 ONCA 812 (CanLII), per Watt JA, at para 240
R v Abbey, 2009 ONCA 624 (ONCA), 246 CCC (3d) 301,  OJ No 3534, per Doherty JA, at para 109
- R v Terceira, 1998 CanLII 2174 (ONCA), (1998) 123 CCC (3d) 1 (ONCA),, per Finlayson JA
- R v M(B), 1998 CanLII 13326 (ONCA), 130 CCC 353 (ONCA), per Rosenberg JA
- Abbey, supra, at para 97 - lower court erred in requiring peer review
- BM, supra ("The fact that a scientific theory is open to debate, however, or that exceptional cases fall outside the norm, does not preclude the admissibility of opinion evidence based on that theory.")
- McWilliams’ Canadian Criminal Evidence (4th) at 12:30.20.50. citing Mohan at 414
- R v Bulman, 2007 ONCA 169 (CanLII),  OJ No 913 (CA), per Gillese JA, at para 7
BM, supra, at para 71
R v Plourde, 2017 ABCA 367 (CanLII), per Slatter JA, at para 6 - ("An expert on drug activity is entitled to develop that expertise by observations of the drug trade, by talking to other experts, and by general involvement in policing of the drug trade.")
Other Qualification Issues
A final draft going to peer review is relevant evidence for disclosure.
Defence Obligation to Disclose
Given the different disclosure obligations between Crown and defence. There may be times where the Crown would need to disclose drafts of the expert reports while defence would not.
The defence however are required to disclose anything that the exported used to form the basis of their opinion.
- R v Natsis, 2018 ONCA 425 (CanLII), at paras 25 to 34
- R v CG, 2018 ONSC 6204 (CanLII), per Bell J
CG, ibid., at para 16 ("... Although the issue in Friskie was the extent to which the Crown was entitled to disclosure of materials provided to a defence expert, it is clear that what the Crown was seeking and what the court ultimately ordered to be disclosed were materials that formed the foundation of the expert’s report. Once an expert witness takes the stand, that witness can no longer be characterized as offering private advice to a party; rather, they are offering an opinion for the assistance of the court and the opposing party must be given access to the foundation of such opinions to test them adequately ..."}}
R v Friskie, 2001 CanLII 392 (SK PC),  205 Sask R 208 (Prov. Ct.)
R v Stone, 1999 CanLII 688 (SCC),  2 SCR 290, per Bastarache J, at para 99(complete citation pending)