Opinion and Expert Evidence
| Author | David M. Paciocco/Lee Stuesser |
| Profession | Justice of the Ontario Court of Justice/Professor of Law, Bond University |
| Pages | 181-216 |
181
CHA PTER 6
OPINION AND
EXPERT EVIDENCE
1. THE gEnER Al ExCluSionA Ry RulE And
iTS ExCEPTionS
“In the law of evidence, an opinion me ans an ‘inference from obser ved
fa ct .’”1 In our system of trial, it is the neutral, impartial trier of fact
who is to determine what inferences to d raw from facts. “A basic tenet
of our law is [therefore] th at the usual witness m ay not give opinion
evidence, but testify only to facts wit hin his knowledge, observation
and experience.”2
In spite of this general exclusionary rule, opinion evidence is often
offered. It is therefore more in structive to focus on when opinion evi-
dence will be allowed. As will be developed in th is chapter, there are
two categories of admissible opinion evidence, one for lay witnesses
and one for expert witnesses. In simple terms, we let lay witnesses offer
opinions when there is no other meaningful way for them to communi-
cate ord inary knowledge t hat they possess. We let expert witnesses
offer opinions where triers of fact do not h ave the special training or
experience required to make the relevant and worthwhile observations
that the witnes s is offering.
It is therefore a straightforwa rd matter as to which set of rules apply
in a given case. If all that is required to form the opinion is ordinary
1 R. v. Collins (2001), 160 C.C.C. (3d) 85 at para. 17 (Ont. C.A.).
2 R. v. D.(D.), [2000] S.C.R. 275 at para. 49.
THE LAW OF EVIDENCE182
experience, the lay opinion rule should be used. For example, the lay
opinion evidence rule governed whether a police officer could testif y to
the direction the person who made footprints in the snow was running,
since “any school child would deduce this from the tracks . . . observed.”3
By contrast if special training or experience is needed to form the opin-
ion, the expert opinion rules apply. For example, evidence predicting
the effects that the pharmaceutical “antabuse” would h ave on alcohol
abuse by an alcoholic had to meet the expert ev idence rules.4
The expert evidence rules a re, of course, intended to determine
when individuals c an offer testimony about things that l ay persons do
not have the special training or experience to observe. As a re sult, the
expert evidence rules that govern opinion evidence are not confined to
opinions per se. Any time a witness offers observations — even descrip-
tive ones — that cannot competently be made without special train-
ing or ex perience, the expert evidence rules descr ibed in this chapter
apply. For example, a lay w itness would not be permitted to descr ibe
the anatomy of the eyeball.
Confusion can be avoided if it is remembered that the issue i n deter-
mining which rules to apply is not whether the witness is an expert. It is
whether the witness, expert or not, is offering informat ion that requires
special training or experience to observe. Accordingly in R. v. Collins
the expert evidence rules did not apply to testimony about the results of
an experiment conducted by police officers to determine whether bul-
lets would r icochet off the w ater, striking a target on the oppo site shore.5
The exper iment did not require expertise to conduct, and no scientific
principles were required to observe the results. Even if the police officers
conducting the experiment had been ballistic experts, expert evidence
rules would not have applied. By contrast, had the officers offered testi-
mony about the speed the bullets travelled when fired from the gun their
testimony would have to comply wit h the expert evidence rules. It is the
substance of the evidence that m atters, not the status of the witne ss.
4 Children’s Aid Society of Simcoe County v. J.D. (2010), 265 O.A.C. 197 (Div. Ct.).
Still, car e has to be taken not to apply the w rong set of rules. In R. v. Ilna (20 03),
172 C.C.C. (3d) 240 (Man. C.A.), for example, the lay opinion rule wa s used to
admit the opinion of p olice officers that the cri me scene had been “staged” to
look like a break-in. Given t hat the court remarked (at para. 79) that profe ssional
experienc e enabled the officers to asse ss the crime scene, it is ar guable that the
expert ev idence rule should have applied. And s ee Arctic Foundations of Canada
Inc. v. Mueller Canada Inc., [2010] 6 W.W.R. 732 (Man. Q.B.) where the trial judge
improperly used the lay opinion rule to exa mine the admission of testimony
about the failure of a t hermosyphon system on t he stability of structur es.
5 Above note 1.
Opinion and Ex pert Evidence 183
2. lAy w iTnESSES
Lay witnesses may present their relevant observations in the form
of opinions where
they are in a better position than the trier of fact to form the •
conclusion;
the conclusion is one that persons of ordinar y experie nce are •
able to make;
the witness, although not ex pert, has the experiential capacity •
to make the conclusion; and
the opinions being expressed are merely a compendious mode of •
stating facts that are too subtle or complicated to be narrated as
effectively without resort to conclusions.
Even for lay witnesse s, the general exclusionary rule disallowing opin-
ion evidence is often not applied. Thi s is because the stark dichotomy
between fact and opinion that is presupposed by the general rule is
unrealistic. As Dickson J. said in Graat v. R.: “Except for the sa ke of
convenience there is l ittle, if any, virtue in any distinction re sting on
the tenuous and frequently fal se antithesis between ‘fact’ and ‘opinion.’
The line between ‘fact’ and ‘opinion’ is not clear.”6 For example, when
a witness identifies the dr iver of the vehicle by pointing her out in
court, he is st ating a s a fact th at she i s the driver. Yet, in a real sense
he is offering his opinion that the person in court is the same p erson
who was driving the vehicle. Numerous apparent statements of fact are
arguably no more t han expre ssions of opinion; things li ke age, height,
weight, the identification of people or things, the speed of vehicles, dis-
tance, whether someone is happy or angr y, all call for judgment to b e
made about what has been obser ved and for conclusions to be draw n.
Obviously, it is common for witnesses to testify about such things. The
fact is that lay wit nesses do offer opinions.
We once proceeded on the basis that there was a general exclu-
sionary rule prohibiting lay witnesses from testif ying about their opin-
ions, to which there were numerous particular exceptions allowing for
proof of the kinds of t hings that have just been described. In Graat 7 the
Supreme Court of Canada adopted a more general, sen sible, and less
technical approach. Graat was charged with impa ired driving, and the
trial judge had permitted a series of witnesses to offer opinion evidence
about whether the ability of Graat to drive a motor vehicle was im-
6 (1982), 31 C.R. (3d) 289 at 305 (S.C .C.).
7 Ibid.
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