As a general rule, opinion evidence is not admissible; witnesses testify as to the facts which they perceived, not as to the inferences – that is, the opinions — that they drew from their perceptions:
Graat v. The Queen, 1982 CanLII 33 (SCC),
 2 S.C.R.
There is, however, an exception for witnesses duly qualified to express an expert’s opinion:
R. v. Abbey, 1982 CanLII 25 (SCC),  2 S.C.R. 24.
The opinion evidence of non‑expert witnesses is generally inadmissible. In R. v. D.D., 2000 SCC 43 (CanLII),  2 S.C.R. 275at para. 49, Justice Major summarized this long-standing exclusionary rule:
A basic tenet of our law is that the usual witness may not give opinion evidence, but testify only to facts within his knowledge, observation and experience. This is a commendable principle since it is the task of the fact finder, whether a jury or judge alone, to decide what secondary inferences are to be drawn from the facts proved.
There is an exception to this rule: the compendious statement of facts exception.
The modern approach to the compendious facts exception was set out by Mr. Justice Dickson in R. v. Graat, 1982 CanLII 33 (SCC),  2 S.C.R. 819. Dickson J. began by noting the tenuous distinction between fact and opinion evidence:
Except for the sake of convenience there is little, if any, virtue, in any distinction resting on the tenuous, and frequently false, antithesis between fact and opinion. The line between “fact” and “opinion” is not clear…
I can see no reason in principle or in common sense why a lay witness should not be permitted to testify in the form of an opinion if, by doing so, he is able more accurately to express the facts he perceived.
Additionally, the Supreme Court of Canada drew a series of conclusions on the admissibility of lay opinion evidence and provided a non-exhaustive list of recognized subjects upon which lay witnesses are allowed to express opinions:
i. the identification of handwriting, persons and things;
ii. apparent age;
iii. the bodily plight or condition of a person, including death and illness;
iv. the emotional state of a person – e.g. whether distressed, angry, aggressive, affectionate or depressed;
v. the condition of things – e.g. worn, shabby, used or new;
vi. certain questions of value; and
vii. estimates of speed and distance.
In R. v. Graat,  2 S.C.R. 819, at 836.
Lay Opinion and Demeanour Evidence
In R. v. H.B, 2016 ONCA 953, the appellant challenged the admissibility of demeanour evidence on the bases that 1. Such evidence was hearsay (see my last blog entry, Is Demeanour Evidence Hearsay?) and 2. It constituted opinion evidence of a non-expert witness (that is, the opinion of a police officer as to the observable emotional state of a person that was not called as a witness at trial).
The Court of Appeal for Ontario determined that because the demeanour evidence fell squarely within item (iv) of the Graat list—evidence of “the emotional state of a person – e.g. whether [a person was] distressed, angry, aggressive, affectionate or depressed”—the police officer’s opinion evidence was admissible.
R. v. H.B., 2016 ONCA 953 at para 75
Demeanour Evidence: Does the Demeanour Evidence Relate to the Accused or a Non-Accused?
In R. v. H.B., the Court rejected the Appellant’s argument that demeanour evidence generally ought not to be admissible, noting that the case law which may support that proposition were cases involving evidence of an accused person’s demeanour, and not what was in question in this case, demeanour evidence of a non-accused person.
R. v. H.B., 2016 ONCA 953 at para 73.