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Evidence - Gate-keeping (Judicial and Adjudicator). R. v. R.G.
In R. v. R.G. (Ont CA, 2026) the Ontario Court of Appeal usefully considers the general admissibility of evidence, judicial gatekeeping - and more specifically the distinction between lay and expert opinion:a. The Governing Principles
[40] The law of evidence distinguishes between observed fact and opinion and, within opinion evidence, between lay and expert opinion.
[41] Observed facts are matters personally perceived by a witness. An opinion involves an inference or conclusion drawn from facts. Where the validity or value of that inference depends upon specialized training, knowledge or experience, the evidence is expert opinion. If the inference does not, then it is lay opinion: R. v. Collins (2001), 2001 CanLII 24124 (ON CA), 160 C.C.C. (3d) 85 (Ont. C.A.), at paras. 16-17.
[42] These distinctions bear directly upon admissibility. Relevant factual evidence is generally admissible unless excluded by a rule of law or because its prejudicial effect exceeds its probative value. Opinion evidence, by contrast, is presumptively inadmissible: Collins, at paras. 16-21; White Burgess Langille Inman v. Abbott and Haliburton Co., 2015 SCC 23, [2015] 2 S.C.R. 182, at para. 14.
[43] Lay opinion may nevertheless be admitted where it is based upon the witness’s own observations, does not depend upon specialized knowledge, and is an inference that the witness is better placed than the trier of fact to draw. Lay witnesses routinely communicate impressions or conclusions that represent convenient ways of describing what they perceived and cannot be readily separated from those underlying observations: Collins, at para. 17; R. v. Graat, 1982 CanLII 33 (SCC), [1982] 2 S.C.R. 819, at pp. 835-39.
[44] Expert opinion is different. It draws its evidentiary force from knowledge or experience outside the ordinary experience of the trier of fact. A witness who proposes to give such evidence must possess appropriate expertise and satisfy the governing requirements for admissibility: White Burgess, at paras. 15, 23-24.
[45] Those safeguards serve an important purpose. Expert evidence carries a particular risk that the trier of fact may defer to the perceived authority of a witness possessing specialized knowledge. The authority associated with professional expertise may cause an opinion to assume greater evidentiary weight than the underlying evidence justifies: White Burgess, at paras. 17-18.
[46] Trial judges, therefore, perform an essential gatekeeping function. They are responsible for maintaining the evidentiary boundaries between fact, lay opinion, and expert opinion that protect the integrity of the trial process: R. v. Sutherland, 2022 MBCA 23, [2022] 5 W.W.R. 189, at para. 39, leave to appeal refused, [2022] S.C.C.A. No. 134; R. v. Sandhu, 2025 SKCA 76, 453 C.C.C. (3d) 110, at paras. 26-27.
[47] Gatekeeping begins with ruling on admissibility, permissible scope, and use. Vetting potential issues in advance of witness testimony is mandatory for expert evidence. It is also “good practice” where a witness with professional qualifications is called to provide factual testimony or lay opinion: R. v. Umeadi, 2023 ONCA 7, at para. 36, leave to appeal refused, [2023] S.C.C.A. No. 171; see also R. v. Moreira, 2023 ONCA 807, 432 C.C.C. (3d) 255, at para. 37.
[48] That gatekeeping responsibility continues throughout the testimony. A witness called to give factual evidence or lay opinion may, during examination-in-chief or cross-examination, move into an area requiring specialized knowledge. Where the evidence raises a material admissibility concern, particularly where the trier of fact may rely upon it as possessing specialized authority, the trial judge should address the issue with the parties and determine its permissible use. Depending on the circumstances, this may include inviting submissions and determining whether the evidence is admissible as factual evidence or lay opinion or instead requires expert qualification: Sutherland, at paras. 38-39, 47; Bruff-Murphy v. Gunawardena, 2017 ONCA 502, 138 O.R. (3d) 584, at paras. 61-66, leave to appeal refused, [2017] S.C.C.A. No. 343; R. v. J.A.A., 2011 SCC 17, [2011] 1 S.C.R. 628, at para. 11.
[49] At the same time, the boundary must be drawn carefully. The mere fact that a witness possesses professional qualifications does not mean that every inference expressed by that witness is expert opinion: Sutherland, at para. 40.
[50] A psychologist, physician, nurse, or police officer may testify to matters personally observed. Such a witness may also express an otherwise admissible lay opinion where the inference does not depend for its validity upon specialized professional knowledge: Sutherland, at para. 40; R. v. Natsis, 2018 ONCA 425, 140 O.R. (3d) 721, at para. 20.
[51] The critical inquiry is, therefore, not simply who the witness is, but what inference the witness is drawing and what gives that inference its evidentiary force: Sutherland, at para. 40.
[52] That distinction has a corollary important to this appeal. If an opinion is truly lay opinion, a witness’s professional credentials cannot properly be used to give that opinion additional authority. Conversely, where the trier of fact relies upon specialized professional knowledge or experience as a reason for accepting an opinion, the trier of fact is treating the evidence as possessing expert authority: Graat, at pp. 840-41.
[53] In a judge-alone trial, the trial judge must, therefore, guard not only against relying upon inadmissible expert opinion, but also against subsequently giving otherwise admissible evidence expert weight because of professional qualifications that have not been established for that purpose: J.A.A., at para. 11; Graat, at pp. 840-41.
[54] The gatekeeping responsibility is not eliminated because counsel failed to object when the evidence was given. Evidence requiring expert qualification does not acquire expert status through silence, oversight, or consent: R. v. K.(A.) (1999), 1999 CanLII 3793 (ON CA), 45 O.R. (3d) 641 (C.A.), at para. 73, n. 8, application for leave to appeal quashed, [2000] S.C.C.A. No. 16; R. v. P.J.C., 2025 ONCA 196, 176 O.R. (3d) 262, at para. 30. . R. v. Oppong
In R. v. Oppong (Ont CA, 2021) the Court of Appeal considered the 'gate-keeping' role of judges:[20] The trial judge then assessed whether the probative value of the proposed evidence outweighed its prejudicial effect. He recognized that the “gatekeeper function does not involve bright lines” and that “it requires an analysis of costs and benefits and sometimes does not yield a straightforward “yes” or “no” answer” (citing Abbey, at para. 79 and R. v. Sheriffe, 2015 ONCA 880, 333 C.C.C. (3d) 330, at paras. 101-103, 108, leave to appeal refused, [2016] S.C.C.A. No. 299). The trial judge reviewed a number of case authorities with respect to the assessment of the costs and benefits of evidence relating to gangs: Abbey; R. v. Riley, [2009] O.J. No. 1374 (Ont. Sup. Ct.); R. v. Williams, 2013 ONSC 1076. He noted that the assessment of the probative value of expert evidence involves consideration of the significance of the particular issue, as well as the reliability of the evidence, including the expert’s methodology, expertise and objectivity, while the cost of the evidence addresses the usual risk of prejudice in expert evidence, as well as the risk of complexity and the abdication of the jury’s function to the expert. The trial judge observed that proving criminal organization offences would inevitably involve bad character evidence. As such, steps must be taken to limit the evidence to what is relevant and necessary, and to give mid-trial and final instructions to place the evidence in context and obviate prejudice.
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