Expert Evidence

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General Principles

Expert opinion is testimonial evidence that gives an opinion on facts perceived by him or another that concerns an issue that is likely outside the experience and knowledge of the trier-of-fact (i.e. a lay person). [1] The expert must have special knowledge in the matter [2] and the opinion must be reasonably necessary to assist the trier-of-fact to make a proper judgment. [3] There must also be no exclusionary rules that would otherwise prohibit the evidence from being given. [4]

A person testifying to specialized knowledge will not necessarily be required to be qualified as an expert. Where they testify to their "factual knowledge" based on their "knowledge, observations and experience".[5]

An expert who testifies to direct observation without opinion is not subject to the opinion rule of exclusion. This evidence is admitted in the same way as eye-witness evidence.[6]

The expert is not to testify to facts, but rather only opinion to allow the trier-of-fact to draw inferences. [7]

Relevance is "a threshold requirement" to admitting expert evidence.[8]

The key requirement for expert evidence is that the expert "possesses special knowledge and experience going beyond that of the trier of fact".[9] As long as the court is satisfied that the witness is sufficiently experienced he should be qualified.[10]

Any deficiencies of the knowledge or opinion simply goes to weight.[11]

The means by which the skill, expertise, or knowledge was acquired goes to weight and not admissibility.[12] It is acceptable to obtain the ability to give an opinion from study, instruction, practical experience or observations. Formal study in not necessary.[13]

An expert in any type of litigation has duties and responsibilities that include:[14]

  1. Expert evidence presented to the court should be, and should be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of litigation.
  2. An expert witness should provide independent assistance to the court by way of objective unbiased opinion in relation to matters within his [or her] expertise. An expert witness . . . should never assume the role of an advocate.
  3. An expert witness should state the facts or assumptions upon which his [or her] opinion is based. He [or she] should not omit to consider material facts which could detract from his [or her] concluded opinion.
  4. An expert witness should make it clear when a particular question or issue falls outside his [or her] expertise.
  5. If an expert's opinion is not properly researched because he [or she] considers [there to be] insufficient data . . . available, then this must be stated with an indication that the opinion is no more than a provisional one. In cases where an expert witness, who has prepared a report could not assert that the report contained the truth, the whole truth and nothing but the truth without some qualification, that qualification should be stated in the report

The expert's right to give opinion evidence imports an obligation of maintaining an attitude of "strict independence and impartiality".[15]

It has been recommended that an "evidence-based approach" be taken to evaluate experts. This suggests four requirements:[16]

  1. the theory or technique utilized by the expert must be reliable, and used in a manner that is reliable;
  2. the expert must keep an open mind to a "broad menu of possibilities" (not be biased);
  3. the expert must be objective and comprehensive in collecting evidence -- including rejecting information not germane and transparent about the information and influences involved; and
  4. the expert must proffer more than the mere opinion, including the complete reasoning process, shortcomings and fair guidance on the confidence in the opinion.

Standard of Review
Trial judges are entitled to "wide discretion" and deference when weighing the costs and benefits of admitting expert evidence.[17]

Whether someone can be qualified as an expert is a question of law and is reviewable on a standard of correctness.[18]

  1. Folkes v Chadd (1782), 3 Dougl. 157
    R v J-L J, [2000] 2 SCR 600, 2000 SCC 51 (CanLII) at para 56
    R v Abbey, 1982 CanLII 25 (SCC), [1982] 2 SCR 24
    R v Mohan 1994 CanLII 80 (SCC), [1994] 2 SCR 9 at 413 (the opinion must "provide information ‘which is likely to be outside the experience or knowledge of’” the trier of fact")
    R v Bunniss (1964), 44 CR 262 (BC Co. Ct.) per Tyrwhitt-Drake (an expert is "one who has by dint of training and practice, acquired a good knowledge of the science or art concerning which his opinion is sought, and the practical ability to use his judgment in that science")
  2. R v Terceira, 1998 CanLII 2174 (ON CA), (1998) 123 CCC 1 (Ont. CA) Mohan, supra at p. 414 (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”)
  3. Mohan, supra
    R v Lovie, 1995 CanLII 801 (ON CA)
  4. R v N.O., 2009 ABCA 75 (CanLII) at para 19
  5. R v Hamilton, 2011 ONCA 399 (CanLII) at paras 273 to 284 - evidence from phone company as to the mechanical workings of cell towers and their relationship to the cell phone
    R v Ranger, 2010 ONCA 759 -- cell phone tower evidence
    c.f. R v Korski, 2009 MBCA 37 -- required expert to testify on cell tower evidence
  6. R v K., A., 1999 CanLII 3793 (ON CA) at para 72
  7. R v Parrott, 2001 SCC 3 (CanLII), [2001] 1 SCR 178
    R v Lavallee, 1990 CanLII 95 (SCC), [1990] 1 SCR 852
  8. Mohan, supra at p. 411
  9. R v Béland, 1987 CanLII 27 (SCC), [1987] 2 SCR 398 at p. 415
    R v Marquard, 1993 CanLII 37 (SCC), [1993] 4 SCR 223 at para 35
    R v Chan, 1993 ABCA 383 (CanLII), (1993), 145 A.R. 304 at para 9
  10. Chan, ibid. at para 9
  11. Chan, ibid. at para 9
  12. Chan at para 9 citing Sopinka, Lederman and Bryant, The Law of Evidence of Canada (1992), at pp. 536‑537: ("As long as the court is satisfied that the witness is sufficiently experienced in the subject matter at issue, the court will not be concerned with whether his or her skill was derived from specific studies or by practical training, although that may affect the weight to be given to the evidence.") R v Rayner, 2000 NSCA 143 (CanLII), 189 N.S.R. (2d) 144
  13. R v Melaragni, (1992), 73 CCC (3d) 348 (Ont. Ct. Gen. Div.)(*no link)
    R v N.O., 2009 ABCA 75 (CanLII) at para 22
  14. Bedford v Canada, 2010 ONSC 4264 (CanLII), at para 100 - upheld on appeal 2013 SCC 72
    see also National Justice Compania Naviera SA v Prudential Assurance Co. (The "Ikarian Reefer"), [1993] 2 Lloyd's Rep. 68 (Q.B. (Comm. Ct.)), at pp. 81-82
  15. Bedford at para 101
  16. see Bedford at para 102 - referencing the Goudge Inquiry
    Professor David Paciocco in "Taking a 'Goudge' out of Bluster and Blarney: an 'Evidence-Based Approach' to Expert Testimony" (2009), 13 Can. Crim. L.R. 135
  17. R v Clark, 2016 ABCA 72 (CanLII), at para 59 to 62
    R v DD, 2000 SCC 43 (CanLII) at para 13
    R v Soni, 2016 ABCA 231 (CanLII) at para 8
    R v Dominic, 2016 ABCA 114 (CanLII) at para 17
    R v Abbey, 2009 ONCA 624 (CanLII) at para 97, leave to appeal to SCC refused
  18. R v Bear (C.W.), 2013 MBCA 96 (CanLII) at para 81

Requirements of Expert Evidence ("Mohan" Test)

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.[1] The qualification process is one of delineating the boundaries of the evidence and the language used. [2]

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.[3] Second, the judge must exercise discretion as a gatekeeper and balance the "potential risks and benefits of admitting the evidence".[4]

Mohan Test
To qualify a person as an expert, the evidence must meet the Mohan requirements:[5]

  1. the opinion must be relevant;
  2. the opinion must be necessary to assist the trier-of-fact to draw the correct inference;
  3. the absence of any other exclusionary rule;
  4. 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".[6]

Discretionary Exclusion of Qualified Expert Evidence
Qualified expert evidence can nonetheless be excluded if:[7]

  1. the evidence would tend to usurp the duty of the trier of fact
  2. the prejudicial effect outweighs the probative value
  3. the time required outweighs its probative value
  4. the cost required outweighs the probative value
  5. 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.[8]

Expert evidence should be expected to be impartial to be admissible. There must not be any bias or appearance of bias.[9]

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".[10] 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".[11]

Where the expert witness was not properly qualified and still gave evidence, their opinion may still be admissible absent objection from the opposing counsel.[12]

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".[13]

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.[14]

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.[15] To avoid this the courts as gatekeepers must watch out for:[16]

  • 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.
  1. R v Preeper and Doyle (1888), 15 SCR 401
  2. R v Abbey, 2009 ONCA 624 (CanLII)
    R v K. A., 1999 CanLII 3793 (ON C.A.)
  3. Abbott at para 23
  4. Abbott, ibid. at para 24
  5. R v Mohan, 1994 CanLII 80 (SCC), [1994] 2 SCR 9
    R v Sekhon, 2014 SCC 15 (CanLII) at para 43
  6. Abbott, supra at para 23
    JLJ, supra at paras 33, 35 to 36, 47
    Trochym, supra at para 27
  7. R v D.D., 2000 SCC 43 (CanLII), [2000] 2 SCR 275
  8. R v Bedford, 2000 CanLII 2487 (ON CA), (2000), 143 CCC 3d 311
  9. R v Docherty, 2010 ONSC 3628 (CanLII), [2010] OJ No. 2460 - father of defence counsel writes psych report, found invalid
  10. R v Strickland, 2013 NLCA 65 (CanLII)
  11. Strickland at para 19
  12. See Opinion Evidence Outside of Qualification below
  13. Sekhon, supra at para 48
  14. Sekhon, supra at para 46
  15. Abbott, supra at para 18
  16. Abbott, supra at para 18


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.[1]

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).[2]

Expert evidence can be relevant where it establishes motive to commit the offence.[3] It can also be relevant ot demonstrate animus towards the victim.[4]

It is not legally relevant for a qualified drug expert to say that they have never encountered a blind drug courier in their investigations.[5]

  1. R v Sekhon, 2014 SCC 15 (CanLII) at para 44
    Mohan at pp. 23-24
  2. R v K.(A.), 1999 CanLII 3793 (ON CA), (1999) 137 CCC 3d 225 (ONCA)
  3. R v Ma, [1978] O.J. No. 1425(*no link)
    R v Boucher, 2000 CanLII 6087 (QC CA)
    R v Wilson and Boswell, 2002 CanLII 49653 (ON SC), (2002), 166 CCC (3d) 294 (Ont. S.C.J.)
  4. R v McLeod, [1982] O.J. No. 59(*no link)
    Wilson and Boswell
  5. Sekhon, supra at para 49


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.[1]

The expert evidence must likely outside the ordinary experience and knowledge of the trier of fact.[2] 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”.[3]

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.[4]

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."[5]

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.[6]

  1. R v B.(R.H.), [1994] 2 SCR 656, 1994 CanLII 127
  2. R v Burns, 1994 CanLII 127 (SCC), [1994] 1 SCR 656 at paras 24-25
    R v Mohan, 1994 CanLII 80 (SCC), [1994] 2 SCR 9, (1994), 89 CCC (3d) 402 (S.C.C.) at pp. 414-415
  3. Mohan, ibid. at p. 23
    R v Sekhon, 2014 SCC 15 (CanLII) at para 45
  4. Abbott, supra at para 21
  5. R v Kelliher (Village of) v Smith, [1931] SCR 672, 1931 CanLII 1 (SCC)
    R v DD, [2000] 2 SCR 275, 2000 SCC 43 (CanLII), at para 57
  6. Mohan, supra at p. 24
    Sekhon, supra at para 45
    R v D.D., 2000 SCC 43 (CanLII), [2000] 2 SCR 275


The burden is upon the party calling the witness to prove on a balance of probabilities that they are a "properly qualified expert".[1]

  1. R v Terceira, 1998 CanLII 2174 (ON CA) aff'd at 142 CCC (3d) 95 (SCC)


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.[1]

  1. R v Klassen, 2003 MBQB 253 (CanLII), [2003] M.J. No. 417 at para 26 - drug expert rejected

Experience and Education

An expert does not have to have practical experience.[1]

The essential requirement is that "he should be skilled ... that which he is called upon to give an opinion."[2]

A formal education such as a university degree is not a necessary requirement to be an expert in an area.[3]

However, the expertise must be gained through some form of study or experience.[4] Deficiencies in expertise will usually go to weight not qualifications.[5]

  1. e.g. R v Morgentaler (No. 2) (1973), 14 CCC (2d) 450 (Que. S.C.)(*no link) - gynecologist testified as expert despite having not practiced for 10 years
  2. R v Korski, 2007 MBQB 184 (CanLII), at para 15 citing McWilliams' Canadian Criminal Evidence
  3. R v Dugandzic [1981] O.J. No. 1, 57 CCC (2d) 517 (Ont. C.A.)(*no link) - chemistry degree not required to identify a still
  4. Dugandzic, supra
    R v Godfrey, 1974 ALTASCAD 43 (CanLII), (1974) 18 CCC (2d) 90 (Alta. S.C.A.D.) at pp. 102-104
  5. R v Marquard, 1993 CanLII 37 (SCC), [1993] 4 SCR 223 at p. 243

Independence and Impartiality

A qualified expert witness has as duty to the court to be "fair, objective and non-partisan".[1] An expert unable or unwilling to fulfill this duty "is not qualified to give expert evidence" and should not be allowed to do so.[2]

A lack of independence has traditionally not been a prerequisite to admissibility. Rather partiality usually goes to weight[3] Some degree of favouritism is expected.[4]

Where the expert evidence is not independent, the weight should correspond to "the degree to which their opinions are supported or contradicted by other evidence and common sense". With "little or no support" the evidence could be rejected.[5]

There is suggestion that the expert's opinion may be inadmissible where the lack of independence creates enough prejudice to warrant exclusion.[6]

In certain circumstances, a voir dire has been required to test the alleged lack of independence against the opinion evidence, in particular the assumptions, known facts, and the level of expertise.[7] But it should not be "advocacy dressed up as expert opinion".[8]

Qualifies of an independent witness should include:[9]

  • expert opinion should be and should be seen to be the independent product of the expert uninfluenced as to form or content by the exigencies of litigation;
  • the expert witness should provide independent assistance to the Court by way of objective unbiased opinion in relation to matters within his expertise. The expert witness should never assume the role of advocate.
  • An expert witness should state the facts or assumptions on which his opinion is based. He should not omit to consider material facts which detract from his concluded opinion
  • An expert witness should make it clear when a particular question or issue falls outside his expertise.
  • If an expert's opinion is not properly researched because he considers that insufficient data is available then this must be stated with an indication that the opinion is no more than a provisional one
  • If after exchange of reports, an expert witness changes his view on a material matter ... such change of view should be communicated ... to the other side without delay and when appropriate to the Court.
  • Where expert evidence refers to photographs, plans, calculations ... survey reports or other similar documents [these] must be provided to the opposite party at the same time as the exchange of reports

A retired police officer, experienced and training in investigating organized biker gangs is acceptable evidence.[10]

However, the appearance of bias on the part of an expert can render his opinion evidence inadmissible.[11]

Impartiality requires that the expert stay within the limits of their expertise and qualify their statements.[12] When stating opinion they should be clear to distinguish their own professional opinion from "more generally accepted scientific knowledge" when they diverge.[13]

Courts are often concerned with impartiality where the expert was involved in the application for a search warrant or the laying of charges.[14]

  1. Burgess Langille Inman v Abbott and Haliburton Co, 2015 SCC 23 (CanLII) at para 2
  2. Abbott, ibid. at para 2
  3. R v Payette, 2010 MBQB 73 (CanLII) at paras 16 to 18 R v Violette, 2008 BCSC 920 (CanLII) at para 106 R v Klassen, 2003 MBQB 253 (CanLII) at para 33
  4. Violette, supra, at para 101
  5. Klassen, supra, at para 32
  6. e.g. Payette, supra
    Abbott, supra at para 37
  7. R v INCO Ltd., 2006 CanLII 14962 (ON SC), (2006), 80 O.R. (3d) 594 (Ont. Sup. Ct.)
  8. Fraser River Pile & Dredge Ltd. v Empire Tug Boats Ltd. (1995), 37 C.P.C. (3d) 119, at p. 126
  9. Payette, supra at para 21
  10. Violette, supra
  11. R v Van Bree, 2011 ONSC 4273 (CanLII)
    R v Kovats, 2000 BCPC 176 (CanLII)
  12. R v Olscamp, 1994 CanLII 7553 (ON SC) at para 24 and 29
  13. Olscamp, at para 24
  14. R v Snowdon, 2016 NSSC 321 at para 25

Novel Sciences

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.[1] The courts must individually distinguish between new sciences and "junk" sciences. As such, needs "special scrutiny". [2]

Novel sciences must only be qualified if it is (1) necessary and (2) reliable[3]

When evaluating scientific evidence, the Court should consider Daubert factors:[4]

  1. falsifiability of the theory
  2. peer review and publication of the theory
  3. known or potential rate of error and the existence of standards controlling the research on which the theory is based and
  4. general acceptance of the methodology underlying the theory in the scientific community.

The evidence can still be admissible even if the scientific theory is open to debate or that there are exceptional cases to the theory.[5]

It is not necessary to establish that the field be one that is subject to "peer review".[6]

Expertise "may be acquired through study".[7]

Depending on the subject, it may not be necessary that the expert have a university degree in the subject to be an expert.[8]

The absence of writing or publications will generally go to weight and not admissibility.[9]

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.[10]

  1. e.g. R v Lavallee, 1990 CanLII 95 (SCC), [1990] 1 SCR 852 battered wife syndrome accepted as science
  2. R v J.(-L.), 2000 SCC 51 (CanLII)
  3. R v Terceira (1998) 123 CCC 3d 1 (ONCA),1998 CanLII 2174
  4. R v J.-L.J., 2000 SCC 51 (CanLII), [2000] 2 SCR 600
  5. R v M.(B.), 1998 130 CCC 353 (ONCA), 1998 CanLII 13326 (ONCA)
  6. R v Abbey (2009), 246 CCC (3d) 301, [2009] O.J. No. 3534, 2009 ONCA 624 (ONCA) at para 97 - lower court erred in requiring peer review
  7. McWilliams’ Canadian Criminal Evidence (4th) at 12:30.20.50. citing Mohan at 414
  8. R v Bulman, 2007 ONCA 169 (CanLII), [2007] O.J. No. 913 (QL) (C.A.) at para 7
  9. R v B.M., 1998 CanLII 13326 (ON CA) at para 71
  10. B.M. ("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.")


A party cannot call more than five witnesses without leave of the court.[1]

Under 657.3, the judge may order compliance, seek particulars, or adjourn. He may not prohibit the witness from testifying who complies with the section.[2]

Under s. 7 of the Canada Evidence Act, where any party intends to "examine as witnesses, professional or other experts entitled according to the law or practice to give opinion evidence, not more than five of such witnesses may be called on either side without the leave of the court or judge or person presiding."

  1. s. 7 of the Canada Evidence Act
  2. R v Horan, 2008 ONCA 589 (CanLII)

Notice to Call Expert Evidence

A party must give notice of intention to an expert witness at trial under s. 657.3 (1). A party intending to call the expert witness must give notice at least 30 days prior to the commencement of trial or within the time set by the judge. [1]

The purpose of this section "is to avoid surprises in expert evidence." The other side must have time to prepare a cross and consider retaining their own expert in rebuttal.[2]

The enactment of 657.3(3) modifies the common law principle that "an accused person need not provide disclosure of his or her defence".[3] It is supposed to "promot[e] the fair, orderly and efficient presentation of the testimony of witnesses".[4]

Section 657.3(3) states:

Notice for expert testimony
(3) For the purpose of promoting the fair, orderly and efficient presentation of the testimony of witnesses,

(a) a party who intends to call a person as an expert witness shall, at least thirty days before the commencement of the trial or within any other period fixed by the justice or judge, give notice to the other party or parties of his or her intention to do so, accompanied by
(i) the name of the proposed witness,
(ii) a description of the area of expertise of the proposed witness that is sufficient to permit the other parties to inform themselves about that area of expertise, and
(iii) a statement of the qualifications of the proposed witness as an expert;
(b) in addition to complying with paragraph (a), a prosecutor who intends to call a person as an expert witness shall, within a reasonable period before trial, provide to the other party or parties
(i) a copy of the report, if any, prepared by the proposed witness for the case, and
(ii) if no report is prepared, a summary of the opinion anticipated to be given by the proposed witness and the grounds on which it is based; and
(c) in addition to complying with paragraph (a), an accused, or his or her counsel, who intends to call a person as an expert witness shall, not later than the close of the case for the prosecution, provide to the other party or parties the material referred to in paragraph (b).

1997, c. 18, s. 80; 2002, c. 13, s. 62.


Notice must be comprised of:[5]

  • "name of the proposed witness"
  • a "description of the area of expertise" and
  • a "statement of the qualifications"

Section 657.3(3)(a) applies to both Crown and defence.[6]

Section 657.3(3)(c) requiring the disclosure of the expert's report no later than the closing of the Crown's case is constitutional and does not violate s. 7 of the Charter.[7]

The notice provisions equally apply for the calling of an expert at a sentencing hearing.[8]

Where the expert report is tendered with expert testimony at a preliminary inquiry it may be treated as a substitute for notice.[9]

Additional Crown Requirements
In addition to the obligations that all parties must follow under section 657.3(3)(a), the Crown must also be obliged under s. 657.3(3)(b) to provide a copy of the expert report, if it exists, or a summary of the anticipated evidence, including an opinion and the grounds of that opinion. The Crown obligation need only be fulfilled within a "reasonable period" before the commencement of trial.

Additional Defence Requirements
The Defence need to provide the Crown under s. 657.3(3)(c) with an expert report, If it exists, or summary of the anticipated evidence, including an opinion and the grounds of that opinion.

The "summary" required under s. 657.3 should set out the “chief points or the sum and substance” of the anticipated evidence.[10] What satisfies this requirement will "depend on the context", but it must " 1) provide a reasonable basis for cross-examination; and 2) avoid surprise and delay."[11]

  1. s. 657.3(3)(a)
    R v Salter, 2005 NSCA 129 (CanLII)
  2. R v Mousseau, 2003 ABQB 624 (CanLII) at para 30
  3. R v Hong, 2015 ONSC 4840 (CanLII) per Boswell SCJ at para 7
  4. Hong, ibid. at para 7
  5. see s. 657.3(3)(a)
    Hong, ibid. at para 8
  6. Hong, supra at para 8
  7. R v Sandham, 2009 CanLII 58981 (ON SC)
  8. R v Gunning, 2007 BCSC 144 (CanLII)
  9. R v Reis, 2010 BCSC 799 (CanLII)
  10. R v Mousseau, 2003 ABQB 624 (CanLII), per Moen SCJ, at para 56
    Hong, supra
  11. Mousseau, ibid. at para 56

Notice of Defence Expert

Section 657.3(3)(c) requires that the defence disclose a copy of the report, if any, a summary of the opinion and the grounds for the opinion of the expert no later than the close of the Crown's case.[1]

There is some suggestion that the Crown is also entitled to the notes and work product of the defence expert to be called.[2]

  1. Prior to enacting s. 657.3(3), at common law the defence did not need to disclose and simply could adjourn cross-examination, see R v Stone, 1999 CanLII 688 (SCC), [1999] 2 SCR 290 at para 147 and comments of Binnie J., joined in by majority at para 228
  2. See Stone

If Notice is Not Given

Section 657.3(4) states that where the notice requirements of s. 657.3(3) are not complied with, the available remedies are:

  • an "adjournment of the proceedings to the party who requests it to allow him or her to prepare for cross-examination of the expert witness;" (657.3(4)(a))
  • an "order the party who called the expert witness to provide that other party and any other party with the material referred to in paragraph (3)(b);" and (657.3(4)(b))
  • an "order the calling or recalling of any witness for the purpose of giving testimony on matters related to those raised in the expert witness’s testimony, unless the court considers it inappropriate to do so." (657.3(4)(c))

These remedies do not include the power to prohibit the party from calling the expert.[1]

  1. R v Horan, 2008 ONCA 589 (CanLII)
    Somerville v R., 2012 NBCA 23 (CanLII)

Preparation of Report

Certain courts view the involvement of counsel in reviewing draft expert reports as inappropriate.[1]

  1. Moore v Getahun, 2014 ONSC 237 (CanLII) - on appeal

Other Use of the Materials

Under s. 657.3 (6), the prosecution is prohibited from using any of the materials given to him by defence for as part of its own case where the expert does not testify except for cross-examination without the consent of the accused. It further cannot be used for any other proceedings. (657.3(7))

Admissibility Without Testimony

Section 657.3 permits a party to adduce expert evidence without the need to have the expert give viva vice evidence:

Expert testimony
657.3 (1) In any proceedings, the evidence of a person as an expert may be given by means of a report accompanied by the affidavit or solemn declaration of the person, setting out, in particular, the qualifications of the person as an expert if

(a) the court recognizes that person as an expert; and
(b) the party intending to produce the report in evidence has, before the proceeding, given to the other party a copy of the affidavit or solemn declaration and the report and reasonable notice of the intention to produce it in evidence.

Attendance for examination
(2) Notwithstanding subsection (1), the court may require the person who appears to have signed an affidavit or solemn declaration referred to in that subsection to appear before it for examination or cross-examination in respect of the issue of proof of any of the statements contained in the affidavit or solemn declaration or report.
1997, c. 18, s. 80; 2002, c. 13, s. 62.



Once the witness is qualified as an expert they are permitted to give evidence in the area for which they were qualified.

The expert must cite the bases on his opinion in order for the trier-of-fact to evaluate the opinion. [1] The expert can use sources and information found in the "scope of his or her expertise"[2] as well as sources outside his knowledge in limited contexts.[3] The "second hand" evidence of texts is not admissible as evidence, but can be used to show the information on which the opinion is based.[4]

An expert may be cross-examined on a text, report or article relating to his area of expertise. [5] The expert can only comment on works they are familiar with. If the expert acknowledges the authority, the examiner may read parts of the document to the witness to the extent that it is accepted as valid. Those confirmed passages will become evidence in the case[6]

A judge may reject the uncontradicted expert evidence as unreasonable. [7] The evidence should not be rejected if there is no contradictory evidence and the opinion is not seriously challenged.[8]

Area of Expertise
The qualified "area of expertise" does not need to articulate the exact subject matter to which they will give evidence. It often sufficient to articulate the general area of knowledge.[9]

  1. R v Neil, 1957 CanLII 70 (SCC), [1957] SCR 685
    R v Grandinetti, 2003 ABCA 307 (CanLII)
    R v Trudel, 1994 CanLII 5397 (QC CA)
  2. R v S.A.B., 2003 SCC 60 (CanLII), [2003] 2 SCR 678 at para 63
  3. R v Anderson (1914), 22 CCC 455(*no link)
    R v Godfrey, 1974 ALTASCAD 43 (CanLII), [1974] 4 W.W.R. 677, 18 CCC (2d) 90 (Alta. C.A.), at pp. 102-104
  4. R v Burns, 1994 CanLII 127 (SCC), [1994] 1 SCR 656
  5. R c Taillefer, 1995 CanLII 4592 (QCCA)
    R v Marquard, 1993 CanLII 37 (SCC), [1993] 4 SCR 223
  6. Marquard (" examining an expert witness on other expert opinions found in papers or books is to ask the witness if he or she knows the work. If the answer is "no", or if the witness denies the work's authority, that is the end of the matter. ...If the answer is "yes", and the witness acknowledges the work's authority, then the witness has confirmed it by the witness's own testimony. Parts of it may be read to the witness, and to the extent they are confirmed, they become evidence in the case.")
  7. R v Prince, (1971), 6 CCC (2d) 183 (Ont. C.A.)
    R v Lambkin, 2002 MBCA 157 (CanLII)
  8. R v Molodowic, 2000 SCC 16 (CanLII), [2000] 1 SCR 420
  9. e.g. R v Rothgordt, 2017 BCCA 230 (CanLII), par. 16

Weight of Opinion

Expert opinion on anything that is not necessary for the trier-of-fact to make findings is not admissible.[1]

The opinion evidence given must be within the qualified field of expertise.[2]

The expert need not have personal knowledge of any facts to give an opinion.[3]

A jury must be instructed that the hearsay evidence of the facts underlying the experts opinion is not admissible for any purpose other than to evaluate the weight of the opinion.[4]

The weight given to an opinion is a question of fact.[5]

The opinion must be specific to the case and not simply in generalities.[6]

Requirements for a Factual Foundation
Before a judge can rely upon an expert opinion, the expert must give evidence on the factual foundation relied upon to form the opinion.[7] Where the underlying facts are not established in evidence, the judge cannot rely upon the opinion.[8]

Evaluating Conflicting Expert Evidence
Where the evidence of multiple experts conflict, it is not a matter of chosing one expert over the other, but rather giving weight to each expert and review the opinions as a whole.[9]

  1. R v Howard, 1989 CanLII 99 (SCC), [1989] 1 SCR 1337
    R v Béland, 1987 CanLII 27 (SCC), [1987] 2 SCR 398 R v Millar, (1989), 49 CCC (3d) 193 (ONCA) at 220
  2. Howard
  3. Preeper and Doyle, 1888 CanLII 56 (SCC), (1888), 15 SCR 401
  4. R v Babcock, 1984 ABCA 291 (CanLII)
  5. R v Smithers, 1977 CanLII 7 (SCC), [1978] 1 SCR 506
  6. R v Li, 1980 CanLII 344 (BC SC)
  7. R v Neil, 1957 CanLII 70 (SCC), [1957] SCR 685
    R v Dietrich, 1970 CanLII 377 (ON CA)
  8. R v Abbey, 1982 CanLII 25 (SCC), [1982] 2 SCR 24 ("Before any weight can be given to an expert's opinion, the facts upon which the opinion is based must be found to exist.")
    R v Morgentaler (No. 2) (1973), 14 C.C.C. (2d) 450 (Que. S.C.)(*no link) R v Lupien, [1970] SCR 263, 1969 CanLII 55 (SCC)
    Howard, supra
    Phillion v R., 1977 CanLII 23 (SCC), [1978] 1 SCR 18
  9. R v Jonkman, 2012 SKQB 511 (CanLII) at para 97
    Toneguzza-Norvell v Burnaby Hospital, 1994 CanLII 106 (SCC), [1994] 1 SCR 114
    Housen v Nikulaison, 2002 SCC 33 (CanLII), [2002] 2 SCR 235

Hypothetical Questions

The opinion evidence can be related by way of hypothetical questions put to the expert.[1] However, the testimony cannot be "oath-helping" evidence.[2]

The hypotheticals can be put to the expert where the facts are not dispute.[3] If the underlying facts are in dispute the opinion cannot remove the fact-finding function of the trier-of-fact.[4] The cross examiner can put to the expert any proven or provable facts to determine whether it alters the confidence of a the opinion.[5]

It can be preferrable to ask questions in hypothetical form on contradictory matters in order to avoid overly influencing the jury's fact-finding process.[6]

The party seeking to rely on an expert opinion based on a hypothetical fact has the burden of establishing those underlying facts.[7]

  1. R v Fiqia, 1994 ABCA 402 (CanLII), (1994) 162 A.R. 117 (C.A.)
  2. R v Reid, 2003 CanLII 14779 (ON C.A.)
  3. R v Bleta, 1964 CanLII 14 (SCC), [1964] SCR 561
  4. R v P.G., 2009 ONCA 32 (CanLII)
  5. R v Kerr, 2000 BCCA 209 (CanLII)
  6. R v Leinen, 2013 ABCA 283 (CanLII)
  7. R v Lavallee, [1990] 1 SCR 852, 1990 CanLII 95 (SCC)
    R v Flight, 2014 ABCA 185 (CanLII)

Ultimate Issue Rule

An expert cannot give an opinion upon on an "ultimate issue" to the case otherwise the expert would usurp the role of the trier-of-fact.[1] Where the facts are not in dispute there is a discretion for the judge to allow the expert to give evidence on the ultimate issue.[2]

A psychologist has been allowed to give evidence on whether a murder was "planned and deliberate".[3] Also whether the accused's condition is a "disease of the mind".[4]

  1. R v Béland, 1987 CanLII 27 (SCC), [1987] 2 SCR 398
  2. Swietlinski v R, 1978 CanLII 56 (ON CA)
  3. R v More, 1963 CanLII 79 (SCC), [1963] SCR 522
  4. R v Cooper, 1979 CanLII 63 (SCC), [1980] 1 SCR 1149

Specific Types of Expert

Drug Expert
A lay person such as an RCMP officer cannot be a reliable expert simply by "conducting numerous casual conversations with drug users or traffickers." This sort of "[a]necdotal evidence cannot be tested or verified hearsay must be supplemented and supported by some form of admissible evidence."[1]

  1. R v Klassen, 2003 MBQB 253 (CanLII), [2003] M.J. No. 417

Example Fields of Qualifications

Opinion Evidence Outside of Qualification

Where a qualified expert testifies to matters directly outside of their area of qualification but is clearly within their area of special knowledge, the evidence can still be accepted absent any objection to the evidence by the opposing side.[1] Likewise, a technical failure to qualify someone who clearly has expertise in the area, absent any objections, should be permitted to give expert evidence.[2]

  1. R v Marquard, 1993 CanLII 37 (SCC), [1993] 4 SCR 223 at pp. 242-44
  2. Marquard at pp. 242-44

Where Technical Evidence Does Not Require Expert Evidence

There is some difference in opinion of whether or not expert qualification is needed to present evidence from cell phone towers.[1] It is generally accepted that even where it is not necessary, it is useful to explain some of the records.[2]

Evidence on the regular functioning of social media websites can in circumstances be accepted without qualification.[3]

  1. R v Hamilton, 2011 ONCA 399 (CanLII) at paras 273 to 284 - evidence from phone company as to the mechanical workings of cell towers and their relationship to the cell phone
    R v Ranger, 2010 ONCA 759 (CanLII) -- cell phone tower evidence accepted without qualification for general location evidence
    c.f. R v Korski, 2009 MBCA 37 -- required expert to testify on cell tower evidence
  2. e.g. R v McBean, 2011 ONSC 3125 (CanLII)
  3. R v Soh, 2014 NBQB 20 (CanLII)

Case Digests

See Also