Legal Principles
Author | John Hollander |
Pages | 3-20 |
legal principles
chapter one
Legal Principles
Admissibility and Gatekeepers
the Canadian law of evidence deal
with admissibility issues and they have confronted many
of the main issues that face trial lawyers concerning experts.
ese advances have resolved the dispute as to whether ex-
perts who have personal knowledge of the case are less able
to provide reliable opinions than are those retained exclu-
sively to give an opinion.
In two major decisions, White Burgess Langille Inman
v Abbott and Haliburton Co and R v Mohan, the Supreme
Court of Canada established the rules of evidence with respect
to experts. ese seminal decisions lay down much-needed
guidance for trial courts and counsel. ey form the back-
bone for the cases discussed in this handbook.
To quote from Justice Cromwell in White Burgess:
[19] . . . Mohan established a basic structure for the
law relating to the admissibility of expert opinion
evidence. That structure has two main components.
2 1994 CanLII 80 (SCC) [Mohan].
First, there are four threshold requirements that the
proponent of the evidence must establish in order
for proposed expert opinion evidence to be admis-
sible: (1) relevance; (2) necessity in assisting the trier
of fact; (3) absence of an exclusionary rule; and (4) a
properly qualified expert . . . . Mohan also underlined
the important role of trial judges in assessing wheth-
er otherwise admissible expert evidence should be
excluded because its probative value was overborne
by its prejudicial effect—a residual discretion to ex-
clude evidence based on a cost-benefit analysis . . . .
[20] Mohan and the jurisprudence since, however,
have not explicitly addressed how this “cost-benefit”
component fits into the overall analysis. The reasons
in Mohan engaged in a cost-benefit analysis with re-
spect to particular elements of the four threshold re-
quirements, but they also noted that the cost-benefit
analysis could be an aspect of exercising the overall
discretion to exclude evidence whose probative value
does not justify its admission in light of its poten-
tially prejudicial effects . . . . The jurisprudence since
Mohan has also focused on particular aspects of ex-
pert opinion evidence, but again without always be-
ing explicit about where additional concerns fit into
the analysis. The unmistakable overall trend of the
jurisprudence, however, has been to tighten the ad-
missibility requirements and to enhance the judge’s
gatekeeping role. [References omitted.]
Here, then, are the rules, as laid down by the Supreme
Court. First, there is the issue of admissibility. Regarding this
issue, there are four factors for consideration by the trial judge:
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