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 (CanLII) -- cell phone tower evidence
    c.f. R v Korski, 2009 MBCA 37 (CanLII) -- 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 CanLII links)
    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, supra 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)



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 CanLII links)
    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]

Evaluating Expert Evidence Without A Conflicting Evidence
A judge need not believe or make any findings of fact based on the testimony of an expert witness due to the failure of the other side to adduce contradicting evidence.[10]

  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 CanLII links) 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
  10. R v Doodnaught, 2017 ONCA 781 (CanLII), per Watt JA, at para 124 (" with the testimony of any witness, a trial judge need not believe or make findings of fact based on the testimony of an expert witness simply because no witness is called by the opposite party or evidence adduced to contradict it")
    R. v. Moke (1917), 1917 CanLII 426 (AB CA), 28 C.C.C. 296 (Alta. S.C., A.D.), at p. 300

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 should generally not give an opinion on an "ultimate issue" to the case otherwise the expert would usurp the role of the trier-of-fact.[1] This is not a strict rule as it should be determined on a case-by-case.[2] 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.[3]

A psychologist has been allowed to give evidence on whether a murder was "planned and deliberate".[4] Also whether the accused's condition is a "disease of the mind".[5]

  1. R v Béland, 1987 CanLII 27 (SCC), [1987] 2 SCR 398
  2. R v Potts, 2018 ONCA 294 (CanLII), at para 47 ("It is worth recalling that no general rule precludes the introduction of expert opinion evidence on the ultimate issue in a criminal trial")
    R v Mohan, 1994 CanLII 80 (SCC), [1994] 2 S.C.R. 9, at pp. 24-25
    R v Bryan (2003), 2003 CanLII 24337 (ON CA), 175 C.C.C. (3d) 285 (Ont. C.A.), at paras. 16-17
    R v Lucas, 2014 ONCA 561 (CanLII), 121 O.R. (3d) 303, at para. 271
  3. Swietlinski v R, 1978 CanLII 56 (ON CA)
  4. R v More, 1963 CanLII 79 (SCC), [1963] SCR 522
  5. 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