R. v Barreira et al., 2017 CanLII 30760 (ON SC)
[99] Justice Charron in Collins discussed the difference between fact and opinion at paras. 16 - 21:
3. The law on the admissibility of experiment evidence
16 Despite the fact that experiment evidence is often, and at times routinely, admitted at trials, there is a paucity of Canadian jurisprudence relating to this kind of evidence. Perhaps this is explained by the fact that experiment evidence often goes unrecognized for what it is: in some cases, it consists of mere factual evidence, much like any other sworn testimony; in other cases, it is a combination of factual and opinion evidence. In either situation, its admissibility is governed by well-established rules of evidence. Indeed, in my view, the key to determining the admissibility of experiment evidence is to keep in mind this distinction between fact and opinion as it is understood in the law of evidence. I will briefly review the applicable principles of law.
17 In the law of evidence, an opinion means an "inference from observed fact": see R. v. Abbey (1982), 1982 CanLII 25 (SCC), 68 C.C.C. (2d) 394 at 409. As stated in Abbey, as a general rule, witnesses testify only as to observed facts and it is then up to the trier of fact to draw inferences from those facts. A lay witness will be permitted to give an opinion only with respect to matters that do not require special knowledge and in circumstances where it is virtually impossible to separate the facts from the inferences based on those facts. A witness testifying that "a person was drunk" is a common example of an opinion that can be provided by a lay witness. See R. v. Graat (1982), 1982 CanLII 33 (SCC), 2 C.C.C. (3d) 365 (S.C.C.) for a review of the law on non-expert opinion. Otherwise, opinion evidence will only be received with respect to matters calling for special knowledge beyond that of the trier of fact. In those cases, an expert in the field may be permitted to provide the judge and jury with an opinion, that is "a ready-made inference which the judge and jury, due to the technical nature of the facts, are unable to formulate" (Abbey at 409). The law as to expert opinion evidence was authoritatively restated in Mohan, supra. Before expert opinion evidence can be admitted, the evidence: (a) must be relevant to an issue in the case; (b) it must be necessary to assist the trier of fact; (c) it must not be subject to any other exclusionary rule; and (d) it must be given by a properly qualified expert.
18 A witness' testimony as to observed facts is, of course, subject to the general principles governing the admissibility of any evidence: relevance and materiality. Relevance is established at law if, as a matter of logic and experience, the evidence tends to prove the proposition for which it is advanced. The evidence is material if it is directed at a matter in issue in the case.1 Hence, evidence that is relevant to an issue in the case will generally be admitted. Indeed, it is a fundamental principle of our law of evidence that any information that has any tendency to prove a fact in issue should be admitted in evidence unless its exclusion is justified on some other grounds: see R. v. Corbett, 1988 CanLII 80 (SCC), [1988] 1 S.C.R. 670 at 715; Morris v. R., 1983 CanLII 28 (SCC), [1983] 2 S.C.R. 190 at 201; and R. v. Seaboyer, 1991 CanLII 76 (SCC), [1991] 2 S.C.R. 577 at 609.
19 The grounds that justify the exclusion of evidence that is otherwise relevant and material form the basis of many of our more specific rules of evidence. The rule against hearsay, the opinion rule and the similar fact rule are a few examples. Quite apart from these specific rules, evidence that is otherwise relevant and material may also be excluded by the exercise of the trial judge's general power to safeguard the fairness of the proceedings. Our law of evidence recognizes the general power of a judge to exclude relevant and material evidence where its probative value is outweighed by the prejudice caused by its admission, provided that where the evidence is tendered by the defence, it should not be excluded on that basis unless the prejudice substantially outweighs the value of the evidence: see Seaboyer, supra, at 390; and R. v. S.C.B. (1997), 1997 CanLII 6319 (ON CA), 119 C.C.C. (3d) 530 at 541 (Ont. C.A.). Prejudice in this context does not mean, of course, that the evidence will be detrimental to the other party's position. Rather, it is related to the detrimental effect that the evidence may have on the fairness and the integrity of the proceedings. For example, the evidence may not be worth receiving if its reliability is clearly outweighed by its potential to mislead or confuse the trier of fact. The evidence could also be excluded where its admission would involve an inordinate amount of time that is not commensurate with its value. See Mohan, supra, at 411.
20 These general principles apply to experiment evidence. A pre-trial experiment can be as simple as driving from one location to another to determine the time it takes to cover the distance in order to substantiate or disprove an alibi, or driving along a particular stretch of road to determine at what point a stop sign becomes visible. The evidence in such cases, provided that it is relevant to an issue in the case, will usually be admitted without argument. It is entirely factual, and its admissibility is only subject to the general principles of relevance, materiality and discretion as discussed earlier. In other cases, the pre-trial experiment may be more complex, requiring particular technical or scientific knowledge to perform, and it may also form the basis of expert opinion evidence in the interpretation of the results. In such cases, the experiment evidence, in so far as the observed facts are concerned, will be subject to the usual principles of relevance, materiality and discretion but, in addition, to the extent that it includes inferences from observed facts, the opinion rule will come into play. In order to be admissible, that part of the experiment evidence that constitutes opinion evidence will have to meet the criteria in Mohan.
21 In a nutshell, experiment evidence, if it is relevant to an issue in the case, should generally be admitted, subject to the trial judge's residuary discretion to exclude the evidence where the prejudice that would flow from its admission clearly outweighs its value. Beyond this, when the evidence requires the making of inferences from observed facts that require special knowledge, the test in Mohan will have to be met before the evidence can be admitted as expert opinion evidence.
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