Evidence - Prejudice. R. v. Schneider
In R. v. Schneider (SCC, 2022) the Supreme Court of Canada considers when to exclude evidence where it's prejudicial effect exceeds it's probative value:
(c) Determine Whether to Use Judicial Discretion to Exclude the Evidence. R. v. Aragon
 Finally, judges must determine whether they should exercise their discretion to exclude evidence by balancing probative value against prejudicial effect. Judges sitting with juries should consider the extent to which any prejudicial effect can be attenuated by appropriate instructions to the jury as to the use to which the evidence can properly be put. In addition, evidence can be excluded where there was a significant unfairness associated with obtaining it, such that it would render the accused’s trial unfair (Mohan; Paciocco, Paciocco and Stuesser, at pp. 47-48; Lederman, Fuerst and Stewart, at ¶¶2.75-2.77; Vauclair and Desjardins, at pp. 905-6). No such consideration arises in the circumstances of this case.
 Probative value relates to the degree of relevance to trial issues and the strength of inference that can be drawn from evidence (R. v. Handy, 2002 SCC 56,  2 S.C.R. 908, at para. 26, citing R. v. Robertson, 1987 CanLII 61 (SCC),  1 S.C.R. 918, at p. 943; Hart, at paras. 94-98). Prejudicial effect relates to the likelihood that a jury will misuse the evidence (Hart, at para. 106; Paciocco, Paciocco and Stuesser, at p. 52). Weighing probative value against prejudicial effect has been referred to as a “cost benefit analysis” (Mohan, at pp. 21-22; Hart, at para. 94; Vauclair and Desjardins, at pp. 905-6).
 As noted, the “cost” associated with the evidence (i.e. the prejudice) can be attenuated by appropriate jury instructions. Proper instructions can effectively equip juries with an understanding of how to use evidence in a judicial manner (R. v. Khill, 2021 SCC 37, at para. 116; R. v. Griffin, 2009 SCC 28,  2 S.C.R. 42, at para. 69).
 A trial judge’s determination that the probative value of evidence outweighs its prejudicial effect is discretionary and should be reviewed with deference (R. v. Araya, 2015 SCC 11,  1 S.C.R. 581, at para. 31; R. v. Shearing, 2002 SCC 58,  3 S.C.R. 33, at para. 73). In addition, appellate courts are to review alleged errors in jury instructions “in the context of the entire charge and of the trial as a whole” (R. v. Jaw, 2009 SCC 42,  3 S.C.R. 26, at para. 32, as cited in Araya, at para. 39) so as to afford trial judges “some flexibility in crafting the language of jury instructions” (Araya, at para. 39). I would underscore the importance of trial judges providing clear analysis on the probative value and prejudicial effect of the evidence to facilitate appellate review.
In R. v. Aragon (Ont CA, 2022) the Court of Appeal considers an example (membership in a motorcycle gang) of prejudicial evidence and how to deal with it [more at para. 55-69]:
 Appropriately, an admissibility voir dire was conducted. Extrinsic evidence linking an accused person to a criminal organization, such as an “outlaw motorcycle gang”, including evidence about that organization itself, is sufficiently discreditable to create prejudice against an accused. The evidence is therefore prima facie inadmissible: R. v. B.(L.) (1997), 1997 CanLII 3187 (ON CA), 116 C.C.C. (3d) 481 (Ont. C.A.), at para. 20; R. v. M.R.S., 2020 ONCA 667, 396 C.C.C. (3d) 172, at paras. 62, 71-72; R. v. Tsigirlash, 2019 ONCA 650, at paras. 23, 25; R. v. Cook, 2020 ONCA 731, 394 C.C.C. (3d) 467, at paras. 40-41; R. v. Phan, 2020 ONCA 298, 387 C.C.C. (3d) 383, at para. 90.. R. v. Howley
 Therefore, “[t]he onus is on the prosecution to satisfy the trial judge on a balance of probabilities that in the context of the particular case the probative value of the evidence in relation to a particular issue outweighs its potential prejudice and thereby justifies its reception”: R. v. Handy, 2002 SCC 56,  2 S.C.R. 908, at para. 55.
In R. v. Howley (Ont CA, 2021) the Court of Appeal considered the balance between probative and prejudicial evidence:
 In balancing the probative value of evidence against its prejudicial effect, courts have come to recognize two well established sources of prejudice: moral prejudice and reasoning prejudice. As the Supreme Court explained in R. v. Handy, 2002 SCC 56,  2 S.C.R. 908, moral prejudice refers to the risk associated with evidence that could paint the accused with the stigma of “bad personhood” and cause the jury to assess the accused’s guilt or innocence on the basis of general propensity or disposition: at paras. 42, 100, and 139. By contrast, reasoning prejudice refers to the risk that evidence will distract the jury from its proper focus on the facts as charged: Handy, at paras. 100, 144 and 146. See also R. v. Lo, 2020 ONCA 622, 393 C.C.C. (3d) 543, at paras. 111-116.. R v Ansari
 Needless cumulative evidence carries a risk of both moral prejudice and reasoning prejudice. As this court explained in R. v. Candir, 2009 ONCA 915, 250 C.C.C. (3d) 139, at para. 60, leave to appeal refused  S.C.C.A No. 8:
Th[e] forensic piling on of evidence by the acre unnecessarily lengthens trials, diffuses their focus and diverts the attention of the trier of fact. Cumulative evidence, whether testimony, exhibits or both, often occupies a borderland around the periphery of the case, adding nothing to the contested issues, preferring instead to suffocate the trier of fact with the uncontroversial or marginal. Beyond the concerns for trial efficiency raised in Candir, a trial judge’s discretion to exclude cumulative evidence may also serve to prevent the prejudicial effect “which the sheer volume and repetition of [certain] evidence would have on the jury”: R. v. Parsons (1996), 1996 CanLII 11073 (NL CA), 146 Nfld. & P.E.I.R 210 (Nfld C.A.), at para. 42. Thus, for example, once a fact has been admitted, a trial judge has discretion to exclude further evidence that proves the same fact by more prejudicial means: R. v. Foreman (2002), 2002 CanLII 6305 (ON CA), 169 C.C.C. (3d) 489 (Ont. C.A.), at para. 29, leave to appeal refused  S.C.C.A. No. 199.
 However, evidence is not prejudicial merely because it increases the chances of conviction: R. v. McMorris, 2020 ONCA 844, at para. 124. The Crown will not necessarily be “piling on” by building a strong case. In deciding whether or not to exclude cumulative evidence, the question is not whether the accused could be convicted with less, but rather whether the prejudicial effect of additional evidence outweighs its probative value, keeping in mind that probative value may diminish with repetition. As with any such balancing of probative value and prejudicial effect, the trial judge’s determination is entitled to a high degree of deference on appeal: R. v. Araya, 2015 SCC 11,  1 S.C.R. 581.
In R v Ansari (Ont CA, 2015) Watt JA usefully stated some basic principles of evidence law and their inter-relation [respecting relevance, admissibility, prejudice and whether evidence is probative]:
 The resolution of this ground of appeal requires consideration and application of fundamental principles of the law of evidence. First, the notion of relevance. And, second, the admissibility rule that excludes relevant and material evidence on the ground that its probative value is exceeded by its prejudicial effect.
 Relevance is not an inherent characteristic of any item of evidence. Relevance exists as a relation between, on the one hand, an item of evidence and, on the other, a proposition of fact that the evidence is offered to prove. Relevance is a matter of everyday experience and common sense. An item of evidence is relevant if, by the application of everyday experience and common sense, it renders the fact it seeks to establish by its introduction slightly more or less probable than the fact would be without it: R. v. Luciano, 2011 ONCA 89 (CanLII), 267 C.C.C. (3d) 16, at para. 204.
 Relevance does not exist in the abstract or in the air: Cloutier v. The Queen, 1979 CanLII 25 (SCC),  2 S.C.R. 709, at pp. 730-732; Luciano, at para. 205. Relevance is also relative; we assess and determine it in the context of the entire case in which the evidence is proffered and the positions of counsel in that case: Cloutier, at pp. 730-732; and Luciano, at para. 205.
 To be relevant, an item of evidence need not prove conclusively the proposition of fact for which it is introduced. Nor does the evidence, to be relevant, need to make the proposition of fact more probable than not. An item of evidence is not irrelevant simply because it can sustain more than one inference. The requirement of relevance is met where the item of evidence reasonably shows, “by the application of everyday experience and common sense[,] that the fact is slightly more probable with the evidence than it would be without it”: Luciano, at para. 206.
 Admissibility is a legal concept. Admissibility rules exclude evidence that is both relevant and material on the basis of some policy consideration that the law regards as of sufficient importance to warrant exclusion of evidence that would otherwise assist the trier of fact in ascertaining the truth of the matter at hand. The rule that excludes relevant and material evidence on the basis that its probative value is outweighed by its prejudicial effect is a rule of admissibility.
 The prejudice component of this general exclusionary discretion may involve either or both of two types of prejudice.
 Moral prejudice refers to the risk of an unfocused trial and a conclusion of guilt based on a prohibited chain of reasoning from a general disposition or propensity to guilt of the offence charged. In other words, a finding of guilt that is based on character, not conduct: R. v. Handy, 2002 SCC 56 (CanLII),  2 S.C.R. 908, at paras. 31 and 139.
 Reasoning prejudice involves the distraction of the trier of fact from their proper focus on the offence charged by the introduction of evidence of other incidents that consume undue time and may be accorded more weight than should be their due: Handy, at para. 31 and 144.
 When invited to exclude relevant, material and otherwise admissible evidence on the basis that its prejudicial effect predominates over its probative value, a trial judge will consider the individual constituents of the rule – probative value and prejudicial effect – and then balance them to determine which predominates.
 The assessment of probative value involves consideration of the strength of the evidence; the extent to which it supports the inferences the proponent seeks to have drawn from it; and the extent to which the matters the evidence tends to prove are at issue in the proceedings: R. v. B. (L.); R. v. G. (M.A.) (1997), 1997 CanLII 3187 (ON CA), 116 C.C.C. (3d) 481 (Ont. C.A.), at para. 23.
 An assessment of prejudicial effect should take into account:
i. the degree of discreditable conduct disclosed by the evidence; A trial judge’s decision about where the balance settles between probative value on the one hand and prejudicial effect on the other is accorded a high degree of deference by appellate courts. Where a trial judge has applied the proper principles, weighed the probative value of the evidence and its potential prejudice and decided the issue of admissibility, appellate courts will not lightly intervene: R. v. Arp, 1998 CanLII 769 (SCC),  3 S.C.R. 339, at para. 42; R. v. Bevan, 1993 CanLII 101 (SCC),  2 S.C.R. 599, at p. 613; R. v. B. (C.R.), 1990 CanLII 142 (SCC),  1 S.C.R. 717, at pp. 733-734; R. v. Samuels, 2013 ONCA 551 (CanLII), 310 O.A.C. 175, at para. 47; B. (L.); G. (M.A.), at para. 51.
ii. the extent to which the proposed evidence may support an inference of guilt on the sole basis of bad character;
iii. the extent to which the evidence may confuse issues; and
iv. the ability of the accused to respond to the evidence.
B. (L.); G. (M.A.), at para. 24.
 A final point concerns prophylactic measures undertaken by the trial judge to reduce the risk of reasoning or moral prejudice. A limiting instruction that explains the proper use of this evidence and enjoins prohibited reasoning is of critical importance in ensuring a fair trial: R. v. Vukelich (1996), 1996 CanLII 1005 (BC CA), 108 C.C.C. (3d) 193 (B.C. C.A.), at para. 51.