Avenues for Challenging Experts

• Author: Eric V. Gottardi/Jennifer A. MacLellan/Michael Lacy/Robin Flumerfelt
• Pages: 47-64

47

3

Avenues for

Challenging

Experts

I. Introduction ............................................. 48

II. Stage One: Admissibility ................................... 49

A. Relevance .......................................... 49

B. Necessity .......................................... 50

C. Exclusionary Rules ................................... 51

D. Qualifications ...................................... 53

E. Probative Value Versus Prejudicial Effect ................. 58

F. Reliability of the Evidence ............................. 59

III. Stage Two: Scope of Opinion ............................... 60

IV. Stage Three: Weight ....................................... 62

A. Credibility .......................................... 62

B. Deficiencies in Opinion .............................. 63

C. Adduce Competing Expert Evidence .................... 63

V. Conclusion .............................................. 64

© [2022] Emond Montgomery Publications. All Rights Reserved.

48 Part I Principles and Procedure

I. Introduction

Expert evidence can have a significant impact on the outcome of a trial and unreli-

ableexpert evidence is a leading cause of wrongful convictions. As a result, where the

opposing party seeks to tender expert evidence, it is important to consider the ways in

which its impact can be minimized. There are three general ways to challenge expert

evidence when it is tendered by the opposing side:

1. Challenge the admissibility of the expert opinion: Argue that an opposing

expert’s evidence fails to satisfy the Mohan criteria,1 namely, that it is unreli-

able or that its probative value is outweighed by its prejudicial effect.

2. Challenge the scope of the expert opinion: Argue that a witness’s evidence

exceeds the scope of their expertise or uses language that is objectionable.

3. Challenge the u se to which the evidence can be put: Argue that the expert evi-

dence should be attributed less or no weight due to deficiencies in the opinion,

the expert’s lack of credibility, or the evidence of a competing expert.

While the three ways to challenge expert evidence are presented as distinct, they

are interrelated. For example, reliability is relevant not only to admissibility, but also

to weight. Similarly, the proper scope of an expert’s testimony is tied to their qualifi-

cations at the admissibility stage.

This chapter outlines ten avenues of inquiry when challenging expert evidence.

While this list is not exhaustive, it should provide a useful starting point for counsel

who seek to minimize the impact of an opposing expert’s opinion at trial.

TEN QUESTIONS TO ASK WHEN

CHALLENGINGEXPERT EVIDENCE

STAGE ONE: ADMISSIBILITY

1. Is the expert opinion relevant?

2. Is the expert opinion necessary?

3. Is the expert opinion barred by an exclusionary rule?

4. Is the expert properly qualified?

• Does the expert lack specialized knowledge?

• Does the expert exhibit bias, partiality, or inf luence?

5. Is the probative value of the opinion outweighed by its prejudicial effect?

6. Is the expert opinion unreliable?

STAGE TWO: SCOPE

7. Does the expert opinion exceed the scope of admissibility?

1 R v Mohan, 1994 CanLII 80, [1994] SCJ No 36 (QL) at paras 17-18.

© [2022] Emond Montgomery Publications. All Rights Reserved.