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

CHAPTER 6

OPINION AND

EXPERT EVIDENCE

1. THE gEnERAl ExCluSionARy RulE And

iTS ExCEPTionS

“In the law of evidence, an opinion means an ‘inference from obser ved

fact.’”1 In our system of trial, it is the neutral, impartial trier of fact

who is to determine what inferences to draw from facts. “A basic tenet

of our law is [therefore] that the usual witness may not give opinion

evidence, but testify only to facts within his knowledge, observation

and experience.”2

In spite of this general exclusionary rule, opinion evidence is often

offered. It is therefore more instructive to focus on when opinion evi-

dence will be allowed. As will be developed in this 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 ordinary knowledge that they possess. We let expert witnesses

offer opinions where triers of fact do not have the special training or

experience required to make the relevant and worthwhile observations

that the witness is offering.

It is therefore a straightforward 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 testify 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 have on alcohol

abuse by an alcoholic had to meet the expert evidence rules.4

The expert evidence rules are, of course, intended to determine

when individuals can offer testimony about things that lay persons do

not have the special training or experience to observe. As a result, 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 experience, the expert evidence rules described in this chapter

apply. For example, a lay witness would not be permitted to describe

the anatomy of the eyeball.

Confusion can be avoided if it is remembered that the issue in deter-

mining which rules to apply is not whether the witness is an expert. It is

whether the witness, expert or not, is offering information 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 matters, not the status of the witness.

3 R. v. Lee (2010), 251 C.C.C.(3d) 346 (Alta. C.A.), aff’d 2010 SCC 52 at para. 6.

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 Evidence183

2. lAy wiTnESSES

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 experience 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 witnesses, the general exclusionary rule disallowing opin-

ion evidence is often not applied. This 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 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.”6 For example, when

a witness identif‌ies the driver of the vehicle by pointing her out in

court, he is stating as a fact that she is the driver. Yet, in a real sense

he is offering his opinion that the person in court is the same person

who was driving the vehicle. Numerous apparent statements of fact are

arguably no more than expressions of opinion; things like age, height,

weight, the identif‌ication of people or things, the speed of vehicles, dis-

tance, whether someone is happy or angry, all call for judgment to be

made about what has been observed and for conclusions to be drawn.

Obviously, it is common for witnesses to testify about such things. The

fact is that lay witnesses do offer opinions.

We once proceeded on the basis that there was a general exclu-

sionary rule prohibiting lay witnesses from testifying about their opin-

ions, to which there were numerous particular exceptions allowing for

proof of the kinds of things that have just been described. In Graat7 the

Supreme Court of Canada adopted a more general, sensible, and less

technical approach. Graat was charged with impaired 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.