Expert Evidence: Judge as Gatekeeper

• Author: Richard D. Schneider
• Pages: 23-36

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A. INTRODUCTION

The objective of any trial, in a very general sense, is to determine “what

happened?” at some earlier point in time. To facilitate that goal, individ-

uals who are believed to have some knowledge of the event are called to

court to answer questions. These individuals are prospective witnesses

at the trial. Generally, witnesses are limited to recounting and testifying

as to what they actually heard, saw, smelled, and felt. From all admissible

information, the trier of fact (either a judge sitting alone or a jury) will de-

termine what happened—the facts. Opinions, or factual inferences, from

witnesses as to what transpired are, generally, not permitted except in

special circumstances.1 Generally, it is for the trier of fact to form opinions

and draw inferences, not for the witness. However, the “expert” witness

may be permitted to give opinion evidence based on provided or assumed

facts because of the expert’s recognized expertise acquired through edu-

cation, research, training, work, or other relevant experience. Therefore,

“lay person” witnesses are direct observers whereas “expert” witnesses

may be indirect “inferors.”

Expert opinion evidence can be an essential link to the “truth,” but

it presents with its own inherent dangers. As many have observed before,

1 R. v. Graat, [1982] 2 S.C.R. 819. There are, however, situations where a lay person may

be permitted to give an opinion. For example, a lay person may provide an opinion

addressing an individual’s degree of impairment at a particular point in time.

CHAPTER 3

Expert Evidence: Judge as

Gatekeeper

Richard D. Schneider