View source for Rules of Evidence for a Qualified Expert

{{fr|Règles_de_preuve_pour_un_expert_qualifié}}
{{Currency2|January|2021}}
{{HeaderOpinions}}
==General Principles==
{{seealso|Qualified Expert Evidence}}
Once the witness is qualified as an expert, they are permitted to give evidence in the area for which they were qualified.  

; Requirement of Citing Sources
The expert must cite the basis of his opinion in order for the trier-of-fact to evaluate the opinion.
<ref>
{{CanLIIRP|Neil|22tpj|1957 CanLII 70 (SCC)|[1957] SCR 685}}{{Plurality}}<br>
{{CanLIIRP|Grandinetti|4pvr|2003 ABCA 307 (CanLII)|178 CCC (3d) 449}}{{perABCA|McFadyen JA}} (2:1)<br>
{{CanLIIRP|Trudel|1p9ln|1994 CanLII 5397 (QC CA)|90 CCC (3d) 318}}{{perQCCA|Brossard JA}}<br>
</ref>
The expert can use sources and information found in the "scope of his or her expertise"<ref>
{{CanLIIRP|SAB|1g3m0|2003 SCC 60 (CanLII)|[2003] 2 SCR 678}}{{perSCC-H|Arbour J}}{{atL|1g3m0|63}}</ref> as well as sources outside his knowledge in limited contexts.<ref>
{{CanLIIRP|Anderson|gcgg2|1914 CanLII 361 (AB CA)|22 CCC 455}}{{perABCA|Harvey J}}<br>
{{CanLIIRP|Godfrey|fp05t|1974 ALTASCAD 43 (CanLII)|[1974] 4 WWR 677, 18 CCC (2d) 90}}{{Plurality}} (2:1){{atps|102-104}}
</ref>  
The "secondhand" evidence of texts is not admissible as evidence but can be used to show the information on which the opinion is based.<ref>
{{CanLIIRP|Burns|1frvk|1994 CanLII 127 (SCC)|[1994] 1 SCR 656}}{{perSCC-H|McLachlin J}}</ref>

; Questions on Reports, Texts, and Articles
An expert may be cross-examined on a text, report or article relating to his area of expertise.
<ref>
{{CanLIIRPC|R c Taillefer|1nk5h|1995 CanLII 4592 (QC CA)|100 CCC (3d) 1}}{{perQCCA|Proulx JA}}<br>
{{CanLIIRP|Marquard|1frx2|1993 CanLII 37 (SCC)|[1993] 4 SCR 223}}{{perSCC-H|McLachlin J}}<br>
</ref>
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<ref>
{{ibid1|Marquard}} ("...in 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.")<br>
</ref>

; Rejecting Uncontradicted Expert Evidence
A judge may reject the uncontradicted expert evidence as unreasonable.
<ref>
{{CanLIIRP|Prince|htwr4|1971 CanLII 1285 (ON CA)|6 CCC (2d) 183}}{{perONCA|Gale CJ}}<br>
{{CanLIIRP|Lambkin|5f67|2002 MBCA 157 (CanLII)|170 Man R (2d) 62}}{{perMBCA|Monnin JA}}<br>
</ref>
The evidence should not be rejected if there is no contradictory evidence and the opinion is not seriously challenged.<ref>
{{CanLIIRP|Molodowic|5262|2000 SCC 16 (CanLII)|[2000] 1 SCR 420}}{{perSCC-H|Arbour J}}</ref>

; Statistical and Anecdotal Evidence
The expert cannot recite statistical evidence of probabilities based on similar events prior to the incident to infer what likely occurred in the incident at issue.<ref>
{{CanLIIRP|Klymchuk|1m3d6|2005 CanLII 44167 (ON CA)|203 CCC (3d) 341}}{{perONCA-H|Doherty JA}}{{atL|1m3d6|46}}<br>
{{CanLIIRP|Shafia|gvdw4|2016 ONCA 812 (CanLII)|341 CCC (3d) 354}}{{perONCA-H|Watt JA}}{{AtL|gvdw4|242}} ("An expert is not entitled to give statistical evidence of probabilities based on prior similar events to support a conclusion about what happened on the occasion that forms the subject-matter of charges")<br>
</ref>

The expert may not give anecdotal evidence concerning prior similar events to suggest an opinion about the event at issue.<ref>
{{ibid1|Shafia}}{{AtL|gvdw4|243}} ("Experts may not give anecdotal evidence gathered from prior experiences in proffering their opinion about conduct on a particular occasion. The evidence lacks legal relevance and is apt to engender significant prejudice, especially when adduced to rebut a defence")<br>
{{CanLIIRP|Sekhon|g35qf|2014 SCC 15 (CanLII)|[2014] 1 SCR 272}}{{perSCC-H|Moldaver J}}{{atsL|g35qf|49| to 50}}
</ref>

; Area of Expertise
The qualified "area of expertise" does not need to articulate the exact subject matter to which they will give evidence. It is often sufficient to articulate the general area of knowledge.<ref>
e.g. {{CanLIIRx|Rothgordt|h494z|2017 BCCA 230 (CanLII)}}{{perBCCA|Frankel JA}}{{atL|h494z|16}}<br></ref>

; Use of Report
It is commonplace for an expert to testify with their reports on hand and refer to them during testimony.<ref>
{{CanLIIRP|Sandham|26cvj|2009 CanLII 58982 (ONSC)|[2009] OJ No 4517 (Ont. SCJ)}}{{perONSC|Heeney J}} ("Experts are routinely permitted to have their reports in front of them as they testify, and to refer to them as they deliver their evidence. Such reports are frequently entered as exhibits.")<br>
</ref>

There is some division of whether an expert report should be filed as an exhibit.<ref>
{{CanLIIRx|Millard and Smich|gs46s|2016 ONSC 1517 (CanLII)}}{{perONSC|Goodman J}} (" Generally speaking, I agree that experts’ reports, per se, ought not to be filed as exhibits.  The evidence is their “in-court” testimony. ")<br>
</ref>

; Offer of Alternate Theories
A crown expert is permitted to offer up alternate theories of causation based on the evidence.<ref>
{{CanLIIRx|Biddersingh|j64qq|2020 ONCA 241 (CanLII)}}{{perONCA|Tulloch JA}}{{atL|j64qq|67}}
</ref>

{{reflist|2}}

==Proper Bounds of Opinion==
It is the duty of the trial judge to ensure that the expert stays within the bounds of their expertise.<Ref>
{{CanLIIRP|Sekhon|g35qf|2014 SCC 15 (CanLII)|[2014] 1 SCR 272}}{{perSCC-H|Moldaver J}}{{atL|g35qf|46}} ("...all trial judges ... have an ongoing duty to ensure that expert evidence remains within its proper scope."), {{AtL-np|g35qf|47}} ("The trial judge must both ensure that an expert stays within the proper bounds of his or her expertise and that the content of the evidence itself is properly the subject of expert evidence.")
</ref>

The "opinion rule" does not prevent an expert from giving evidence of fact. The expert may express any firsthand observations that are relevant.<REf>
{{CanLIIRP|Abbey|1lpcd|1982 CanLII 25 (SCC)|[1982] 2 SCR 24}}{{perSCC|Dickson J}} at p. 42<Br>
{{CanLIIR|Sheriffe|gmjcq|2015 ONCA 880 (CanLII)}}{{TheCourtONCA}}{{atL|gmjcq|106}} ("The opinion rule does not bar an expert from giving evidence of fact: Abbey 1982, at p. 42. Put another way, an expert is not confined by the opinion rule to expressing opinions only. The expert is entitled to give evidence of firsthand observations, including for example, those made during a psychiatric interview by a psychiatrist called to proffer an opinion on criminal responsibility.")<br>
</ref>

; Anecdotal Evidence 
The recitation of "anecdotal" evidence about the expert's experience and what the expert has and has not seen carries with it a high degree of prejudice and may result in an error if relied upon for conviction.<REf>
{{ibid1|Sekhon}}<br>
</ref>
While it may be logically relevant, it is not legally relevant whether the expert had encountered other accused in the past who were guilty of an offence.<ref>
{{CanLIIRP|Cook|jbm3n|2020 ONCA 731 (CanLII)}}{{perONCA|Trotter JA}}{{atL|jbm3n|100}}
</ref>
The trier of fact should not reason from a generalized conclusion based on prior experience to a specific state of mind of the person charged.<ref>
{{CanLIIRP|Burnett|hvbfd|2018 ONCA 790 (CanLII)|367 CCC (3d) 65}}{{perONCA-H|Watt JA}}{{atL|hvbfd|75}}<Br>
{{supra1|Cook}}{{atL|jbm3n|100}}
</ref>

Anecdotal evidence is also often not necessary as individual experience may not be beyond the common knowledge and experience of a judge or a matter of technical or scientific in nature.<Ref>
{{supra1|Cook}}{{atL|jbm3n|101}}<br>
{{supra1|Sekhon}}{{AtL|g35qf|49}}
</ref>

{{reflist|2}}

==Weight of Opinion==
Expert opinion on anything that is not necessary for the trier-of-fact to make findings is not admissible.<ref>
{{CanLIIRP|Howard|1ft53|1989 CanLII 99 (SCC)|[1989] 1 SCR 1337}}{{perSCC|Lamer J}}<br>
{{CanLIIRP|Béland|1ftm1|1987 CanLII 27 (SCC)|[1987] 2 SCR 398}}{{perSCC-H|McIntyre J}}
{{CanLIIRP|Millar|gb34s|1989 CanLII 7151 (ON CA)|49 CCC (3d) 193}}{{perONCA-H|Morden JA}}, at 220<br>
</ref>

The opinion evidence given must be within the qualified field of expertise.<ref>
{{supra1|Howard}}<br>
{{supra1|Millar}} <br>
</ref>

The expert does not need to have personal knowledge of any facts to give an opinion.<ref>
{{CanLIIRP|Preeper and Doyle|ggx87|1888 CanLII 56 (SCC)|15 SCR 401}}{{Plurality}}
</ref>

The weight given to an opinion is a question of fact.<ref>
{{CanLIIRP|Smithers|1mk9r|1977 CanLII 7 (SCC)|[1978] 1 SCR 506}}{{perSCC|Dickson J}}
</ref>

The opinion must be specific to the case and not simply in generalities.<ref>
{{CanLIIRP|Li|23m2k|1980 CanLII 344 (BC SC)|59 CCC (2d) 79}}{{perBCSC-H|Trainor J}}
</ref>

; Hearsay
Where a factual premise of an expert is established solely by an out-of-court statement, the opinion can be entitled to less weight and sometimes no weight at all.<ref>
{{CanLIIR|Sheriffe|gmjcq|2015 ONCA 880 (CanLII)}}{{TheCourtONCA}}{{AtL|gmjcq|105}}<br>
{{CanLIIRP|Abbey|1lpcd|1982 CanLII 25 (SCC)|[1982] 2 SCR 24}}{{perSCC|Dickson J}} at p. 46<bR>
R. v. Lavallee, 1990 CanLII 95 (SCC), [1990] 1 S.C.R. 852, at p. 893
</ref>

A jury must be instructed that the hearsay evidence of the facts underlying the expert's opinion is not admissible for any purpose other than to evaluate the weight of the opinion.<ref>
{{CanLIIRP|Babcock|2dgrk|1984 ABCA 291 (CanLII)|16 CCC (3d) 26}}{{perABCA-H|Moir JA}}
</ref>

; 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.<ref>
{{CanLIIRP|Neil|22tpj|1957 CanLII 70 (SCC)|[1957] SCR 685}}{{Plurality}}<br>
{{CanLIIRP|Dietrich|g1bt2|1970 CanLII 377 (ON CA)|1 CCC (2d) 49 }}{{perONCA-H|Gale CJ}}<br>
</ref>
Where the underlying facts are not established in evidence, the judge cannot rely upon the opinion.<ref>
{{CanLIIRP|Abbey|1lpcd|1982 CanLII 25 (SCC)|[1982] 2 SCR 24}}{{perSCC|Dickson J}} ("Before any weight can be given to an expert's opinion, the facts upon which the opinion is based must be found to exist.")<br>
{{CanLIIRP|Morgentaler|htxsb|1973 CanLII 1462 (QC CQ)|14 CCC (2d) 450}}{{perQCCQ|Hugessen ACJ}}
{{CanLIIRP|Lupien|1xd5k|1969 CanLII 55 (SCC)|[1970] SCR 263}}{{Plurality}}<br>
{{supra1|Howard}}<br>
{{CanLIIRP|Phillion|1tx3f|1977 CanLII 23 (SCC)|[1978] 1 SCR 18}}{{perSCC|Ritchie J}}<br>
</ref>

The evidence relied upon for the opinion can include second-hand evidence, but that it may affect the weight accorded to the opinion.<ref>
{{CanLIIRP|Alcantara|fqvvj|2012 ABQB 225 (CanLII)|538 AR 44}}{{perABQB|Greckol J}}{{atL|fqvvj|125}}<br>
</ref>

; Evaluating Conflicting Expert Evidence
Where the evidence of multiple experts conflict, it is not a matter of choosing one expert over the other but rather giving weight to each expert and reviewing the opinions as a whole.<ref>
{{CanLIIRP|Jonkman|fvfwq|2012 SKQB 511 (CanLII)|410 Sask R 171}}{{perSKQB|Schwann J}}{{atL|fvfwq|97}}<br>
{{CanLIIRPC|Toneguzza-Norvell v Burnaby Hospital|1frwb|1994 CanLII 106 (SCC)|[1994] 1 SCR 114}}{{perSCC-H|McLachlin J}}<br>
{{CanLIIRPC|Housen v Nikulaison|51tl|2002 SCC 33 (CanLII)|[2002] 2 SCR 235}}{{perSCC|Iacobucci and Major JJ}}<br>
</ref>

; 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.<ref>
{{CanLIIRP|Doodnaught|h6m5m|2017 ONCA 781 (CanLII)|358 CCC (3d) 250}}{{perONCA-H|Watt JA}}{{atL|h6m5m|124}} ("...as 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")<br>
{{CanLIIRP|Moke|gw70b|1917 CanLII 426 (AB CA)|28 CCC 296 (Alta. S.C., A.D.)}}{{perABCA-H|Walsh J}}{{atp|300}}<br>
</ref>

{{reflist|2}}

==Hypothetical and Generic Questions==
The opinion evidence can be related by way of hypothetical questions put to the expert.<ref> 
{{CanLIIRP|Fiqia|2dbft|1994 ABCA 402 (CanLII)|(1994) 162 AR 117 (CA)}}{{perABCA|Hunt JA}}</ref> 
However, the testimony cannot be "oath-helping" evidence.<ref> 
{{CanLIIRP|Reid|6g6g|2003 CanLII 14779 (ON CA)|177 CCC (3d) 260}}{{perONCA|Moldaver JA}}</ref> 

The hypotheticals can be put to the expert where the facts are not in dispute.<ref>
{{CanLIIRP|Bleta|1tvsq|1964 CanLII 14 (SCC)|[1964] SCR 561}}{{perSCC|Ritchie J}}</ref>  If the underlying facts are in dispute the opinion cannot remove the fact-finding function of the trier-of-fact.<ref>
{{CanLIIRP|PG|224d8|2009 ONCA 32 (CanLII)|242 CCC (3d) 558}}{{perONCA|Juriansz JA}}</ref>
The cross-examiner can put to the expert any proven or provable facts to determine whether it alters the confidence of the opinion.<ref>
{{CanLIIRP|Kerr|533d|2000 BCCA 209 (CanLII)|32 CR (5th) 359}}{{perBCCA|McEachern CJ}}</ref>

It can be preferable to ask questions in hypothetical form on contradictory matters in order to avoid overly influencing the jury's fact-finding process.<ref>
{{CanLIIRP|Leinen|g01l8|2013 ABCA 283 (CanLII)|301 CCC (3d) 1}}{{perABCA|Hunt JA}} (2:1){{AtL|g01l8|24}} ("Using hypotheticals when dealing with experts is preferred (especially when there is contradictory evidence) because that is said to remove the danger of an expert overly influencing the jury’s fact-finding mission. When the hypothetical question technique is not used, careful instructions to the jury are required...")
</ref>
Where hypotheticals are not used in contradicting an expert, "careful instructions" are required.<Ref>
{{ibid1|Leinen}}{{atL|g01l8|24}}<Br>
{{CanLIIRP|PG|224d8|2009 ONCA 32 (CanLII)|242 CCC (3d) 558}}{{perONCA|Juriansz JA}}{{AtsL|224d8|29| to 30}}, 244 OAC 316{{fix}}<br>
{{CanLIIRP|Kelly|gbr94|1990 CanLII 11053 (ON CA)|41 OAC 32, 59 CCC (3d) 497}}{{perONCA|Finlayson JA}}
</ref>

The party seeking to rely on an expert opinion based on a hypothetical fact has the burden of establishing those underlying facts.<ref>
{{CanLIIRP|Lavallee|1fsx3|1990 CanLII 95 (SCC)|[1990] 1 SCR 852}}{{perSCC|Wilson J}}<br>
{{CanLIIRP|Flight|g711g|2014 ABCA 185 (CanLII)|313 CCC (3d) 442}}{{perABCA|Veldhuis JA}}<br>
</ref>

; Generic questions
Generic evidence about practices can be necessary to assist the jury.<ref>
{{CanLIIRP|Solleveld|g6xv9|2014 ONCA 418 (CanLII)|311 CCC (3d) 387}}{{TheCourtsONCA}}{{atL|g6xv9|19}}

</ref>

{{reflist|2}}

==Ultimate Issue Rule==
Traditionally, an expert should not give an opinion on an "ultimate issue" to the case; otherwise, the expert would usurp the role of the trier-of-fact.<ref>
{{CanLIIRP|Béland|1ftm1|1987 CanLII 27 (SCC)|[1987] 2 SCR 398}}{{perSCC-H|McIntyre J}}
</ref>
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.<ref>
{{CanLIIRPC|Swietlinski v R|1vm6l|1978 CanLII 56 (ON CA)|44 CCC (2d) 267}}{{perONCA-H|Martin JA}}
</ref>

In modern application, this rule has largely disappeared.<Ref>
{{CanLIIRxC|Hamilton v Bluewater Recycling Association|gvflq|2016 ONCA 805 (CanLII)}}{{TheCourtONCA}}{{atL|gvflq|21}} ("there is no longer a general prohibition on the admission of expert evidence concerning the ultimate issue")<br>
{{CanLIIRP|Lucas|g84mv|2014 ONCA 561 (CanLII)|121 O.R. (3d) 303, 313 CCC (3d) 159}}{{TheCourtONCA}} leave to appeal refused, [2014] S.C.C.A. No. 460, at para. 271<br>
{{CanLIIRPC|Hoang v Vicentini|gtzvf|2016 ONCA 723 (CanLII)|352 OAC 358}}{{perONCA|Brown JA}}{{atL|gtzvf|62}}<br>
{{CanLIIRP|Solleveld|g6xv9|2014 ONCA 418 (CanLII)|311 CCC (3d) 387}}{{TheCourtONCA}}{{AtL|g6xv9|18}} ("The Supreme Court of Canada has repeatedly affirmed that the common law rule precluding expert evidence on the ultimate issue no longer applies in Canada")<br>
{{CanLIIRP|Burns|1frvk|1994 CanLII 127 (SCC)|[1994] 1 SCR 656}}{{perSCC-H|McLachlin J}}{{AtL|1frvk|25}} ("While care must be taken to ensure that the judge or jury, and not the expert, makes the final decisions on all issues in the case, it has long been accepted that expert evidence on matters of fact should not be excluded simply because it suggests answers to issues which are at the core of the dispute before the court")<Br>
{{CanLIIRP|Bryan|6xxg|2003 CanLII 24337 (ON CA)|175 CCC (3d) 285}}{{perONCA|Goudge JA}}{{AtL|6xxg|16}} ("there is now no general rule precluding expert evidence on the ultimate issue")<Br>
{{CanLIIRx|Potts|hr64n|2018 ONCA 294 (CanLII)}}{{TheCourtONCA}}{{atL|hr64n|47}} ("It is worth recalling that no general rule precludes the introduction of expert opinion evidence on the ultimate issue in a criminal trial")<br>
{{CanLIIRP|Mohan|1frt1|1994 CanLII 80 (SCC)|[1994] 2 SCR 9}}{{perSCC-H|Sopinka J}}{{atps|24-25}}<br>
{{CanLIIRP|Bryan|6xxg|2003 CanLII 24337 (ON CA)|175 CCC (3d) 285}}{{perONCA-H|Goudge JA}}{{atsL|6xxg|16| to 17}}<br>
{{CanLIIRP|Lucas|g84mv|2014 ONCA 561 (CanLII)|121 OR (3d) 303}}{{TheCourtONCA}}{{atL|g84mv|271}}<br>
</ref>

However, the trial judge must apply "increased scrutiny" of the relevance and necessity when the evidence approaches the ultimate issue.<ref>
{{supra1|Solleveld}}{{atL|g6xv9|20}}<br>
{{supra1|Mohan}}{{atsL|1frt1|24| to 25}}<Br>
</ref>

; Example
A psychologist has been allowed to give evidence on whether a murder was "planned and deliberate."<ref>
{{CanLIIRP|More|22vz3|1963 CanLII 79 (SCC)|[1963] SCR 522}}{{perSCC|Cartwright J}}
</ref>
Also, whether the accused's condition is a "disease of the mind."<ref>
{{CanLIIRP|Cooper|1tx9m|1979 CanLII 63 (SCC)|[1980] 1 SCR 1149}}{{perSCC|Dickson J}}
</ref>
{{reflist|2}}

==Change of Opinion==
It is accepted that the testimony of witnesses, expert or otherwise, may change over time for various reasons. A mistrial would likely not be available where a witness gives advance notice that their evidence has changed.<ref>
{{CanLIIRx|Chen|j0dx2|2019 ONSC 3088 (CanLII)}}{{AtL|j0dx2|22}} ("Given this undeniable reality in criminal trials, it is difficult to imagine circumstances where it would be necessary to declare a mistrial simply because a witness gave advance notice to the lawyer who was planning on calling them, that they were going to, in fact, give unanticipated testimony at variance with some earlier indication of what their testimony might be.")
</ref> 

{{reflist|2}}

==Specific Types of Expert==
; Drug Expert
A layperson 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."<ref>
{{CanLIIRP|Klassen|26j|2003 MBQB 253 (CanLII)|[2003] MJ No 417}}{{perMBQB|Scurfield J}}</ref>

; Financial Expert
In a financial crime case, it can be appropriate for the Crown to lead "generic" evidence as to "legitimate and illegitimate ... banking practices and documents."<Ref>
{{CanLIIRP|Solleveld|g6xv9|2014 ONCA 418 (CanLII)}}{{TheCourtONCA}}{{atL|g6xv9|19}}
</ref>

{{Reflist|2}}