Evidence - Basics
Evidence - Opinion Rule
Evidence - Browne v Dunn
R v Vassel (Ont CA, 2018)
In this case the Court of Appeal reviews, in turn, basic principles of evidence law, the opinion rule and the rule Browne v Dunn:
 Relevance. An item of evidence is relevant if it renders the fact it seeks to establish by its introduction slightly more or less probable than that same fact would be without that evidence. Relevance is a matter of everyday experience and common sense. It is assessed in the context of the entire case and the positions of counsel: R. v. Luciano, 2011 ONCA 89 (CanLII), 267 C.C.C. (3d) 16, at paras. 204-206.
 Materiality. An item of evidence is material if it is offered to prove or disprove a fact in issue: Luciano, at para. 207. Whether an accused said to have committed an offence as a principal was present at the scene of the offence is a fact in issue.
 Admissibility. Relevant and material evidence is admissible if it satisfies all the existing tests and extrinsic policies of the law of evidence, whether based on common law principles, statutory provisions or constitutional precepts: Luciano, at para. 209; R. v. Zeolkowski, 1989 CanLII 72 (SCC),  1 S.C.R. 1378, at p. 1386.
 The admissibility rule said to be applicable here is the opinion rule. Like its siblings, hearsay and character, the opinion rule is exclusionary by nature. It insists that witnesses give evidence of facts, not make statements of opinions or inferences drawn from those facts. It follows, at least as a general rule, that evidence of a witness’s opinion is not admissible: White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23 (CanLII),  2 S.C.R. 182, at para. 14. The most convincing rationale for the rule is that these ready-formed inferences offered by the witness are unhelpful to the trier of fact and might be misleading: R. v. Graat, 1982 CanLII 33 (SCC),  2 S.C.R. 819, at p. 836. See also White Burgess, at para. 14.
 As with other admissibility rules, the opinion rule is not unyielding. Not all opinion evidence is excluded. We recognize that, so far as matters that require special knowledge or skill are concerned, triers of fact, whether judges or jurors, are not necessarily equipped to draw true inferences from facts stated by witnesses. Assistance is necessary. And so it is that we permit witnesses to state their opinions about these subjects, provided the witnesses are shown to be experts in them: White Burgess, at para. 15; R. v. Abbey, 1982 CanLII 25 (SCC),  2 S.C.R. 24, at p. 42.
 Where the opinion rule is put forward as the ground upon which evidence proposed for admission should be excluded, the judge embarks upon a two-step inquiry into admissibility: White Burgess, at para. 22; see also, R. v. Abbey, 2009 ONCA 624 (CanLII), 97 O.R. (3d) 330, at para. 76, leave to appeal refused,  S.C.C.A. No. 125 (“Abbey ‘09”).
 At the first step of the admissibility inquiry, the proponent of the evidence must establish the threshold requirements of admissibility. These are the four Mohan factors:
iii. the absence of an exclusionary rule; and
iv. a properly qualified expert.
See White Burgess, at para. 23; R. v. Mohan, 1994 CanLII 80 (SCC),  2 S.C.R. 9, at p. 20; R. v. Bingley, 2017 SCC 12 (CanLII),  1 S.C.R. 170, at paras. 14-15.
 At this first step, the relevance factor refers to logical relevance: White Burgess, at para. 23; Abbey ‘09, at para. 84. The necessity requirement endeavours to ensure that the potential of expert opinion evidence to distort the fact-finding process is not lightly tolerated. White Burgess, at para. 21; R. v. D.D., 2000 SCC 43 (CanLII),  2 S.C.R. 275, at para. 46 and 57. As a result, the opinion evidence is unnecessary if on the facts established by other evidence the trier of fact can reach their own conclusion about the issue to which the proposed opinion evidence is directed without that opinion: Sekhon, at para. 45. What is required is that the opinion proposed for admission provide information that is likely to be outside the experience and knowledge of a jury: Mohan, at p. 23. Mere relevance or helpfulness is not enough: R. v. D.D., at para. 46.
 Under Mohan, a duly qualified expert is a witness who by study or experience has acquired special or peculiar knowledge of a subject about which a party proposes the witness will testify: Mohan, at p. 25. As we have seen, the extent of knowledge of the proposed expert must exceed the knowledge and experience of the trier of fact about the same subject: Bingley, at para. 22.
 It is the responsibility of the party who seeks to elicit expert opinion evidence from a proposed (or actual) witness to qualify the witness as an expert in the subject-matter about which the opinion is to be elicited: R. v. Marquard, 1993 CanLII 37 (SCC),  4 S.C.R. 223, at p. 243. It is the obligation of opposing counsel to object where appropriate and the task of the trial judge to ensure that the expert stays within the scope of his or her expertise: Marquard, at p. 244; Abbey ‘09, at para. 62; Sekhon, at paras. 46-47.
 At the second or gatekeeping step, the trial judge must balance the risks and benefits of admitting the evidence, thereby to determine whether the proposed evidence is sufficiently beneficial to the trial process to warrant its admission despite the potential harm to that same trial process that may flow from the admission of the expert evidence: White Burgess, at para. 24; Abbey ‘09, at para. 76. Relevance, necessity, and reliability, as well as the expert’s independence and impartiality, continue to play a role in weighing the overall competing considerations in admitting the evidence: White Burgess, at para. 54.
 Sometimes in giving evidence at trial, an expert may give opinions that extend beyond the subjects on which the expert has been qualified to give evidence. To the extent that an expert does so, the unqualified opinions are to be disregarded by the trier of fact. Where the trier of fact is a jury, the trial judge should instruct them accordingly: Marquard, at p. 244; Sekhon, at para. 48.
 A final point concerns anecdotal evidence, which sometimes enters the record of trial proceedings during the testimony of an expert. Anecdotal evidence is testimony that does not speak to the facts of the case but reasons from the witness’s prior experience to the probability of a particular result or occurrence in the case at hand. Anecdotal evidence is not legally relevant. Nor is it necessary. It lacks probative value. It is inherently prejudicial and tends to shift the onus of proof to an accused: Sekhon, at paras. 41, 49 and 50.
 To begin, the rule in Browne v. Dunn (1894), 1893 CanLII 65 (FOREP), 6 R. 67.
 The rule is one of fairness, thus not a fixed or invariable rule, much less a rule of admissibility. The extent of its application rests within the sound discretion of the trial judge, a discretion that is subject to significant deference on appeal: R. v. Quansah, 2015 ONCA 237 (CanLII), 125 O.R. (3d) 81, at paras. 76-77 and 80, leave to appeal refused,  S.C.C.A. No. 203
 Compliance with the rule in Browne v. Dunn requires a cross-examiner to confront the witness with matters of substance, not inconsequential detail, on which the cross-examining party seeks to impeach the witness and call contradictory evidence: Quansah, at para. 81. When it is apparent from the tenor of counsel’s cross-examination of a witness that the cross-examiner does not accept the witness’s version of events, the confrontation is general and known to the witness, and the witness’ view on the contradictory matter is apparent, specific confrontation of the witness is not necessary: Quansah, at para. 82.
 As a rule of fairness, no fixed relation exists between a breach of the rule in Browne v. Dunn and the remedy available for that breach. No single or exclusive remedy follows from the breach. It is for the trial judge to say what remedy is best suited to maintain fairness in the trial process: Recall of the witness, for instance. A jury instruction about the impact of the failure to cross-examine on the jury’s assessment of credibility and reliability. Or something else entirely. A remedy decision also attracts deference on appeal: Quansah, at paras. 117-118.