Expert Evidence - 'The 7 Deadly Sins' #2 - Trying To Fit Square Pegs Into Round Holes

The courts have been consistent and clear that expert evidence is permissible to assist in limited circumstances. In the seminal case R. v. Mohan:1

"Admission of expert evidence depends on the application of the following criteria:

(a) relevance;

(b) necessity in assisting the trier of fact;

(c) the absence of any exclusionary rule; and,

(d) a properly qualified expert."

and in Rice v. Sockett:2

"The derivation of the term 'expert' implies that he is one who by experience has acquired special or peculiar knowledge of the subject of which he undertakes to testify, and it does not matter whether such knowledge has been acquired by study of scientific works or by practical observation. Hence, one who is an old hunter, and has thus had much experience in the use of firearms, may be as well qualified to testify as to the appearance which a gun recently fired would present as a highly-educated and skilled gunsmith."

If the relevance, necessity and expertise of the expert are not established and precisely communicated to the court during the qualification process, the range of the expert's subsequent testimony may be restricted by sustained objections from opposing counsel, leaving you with an unplanned void in the evidentiary foundation of your case.

Trouble is not far off if:

1. The right questions are asked, but to the wrong expert; or,

2. The right expert is asked to give an opinion on the wrong questions/issues.

   Trouble can come in three principal forms:

1. Ill-conceived Marching Orders

   In several cases, I have been faced with a series of cross examination questions regarding an instruction letter I received – an avoidable distraction;

   On the surface, informing the expert as to the mandate, and the substance and timing of deliverables seems relatively straight forward, and in years gone by this was probably true. But in today's environment of more fulsome disclosure, the expert's file (including communications with counsel) may be available to opposing counsel at some point in the proceedings. It is important to keep this in mind during all your dealings with your expert.

   Initial instructions and subsequent communications between counsel and the expert can be verbal or written and general or detailed.

   A more general mandate may involve, for example, a brief discussion over the phone whereby the expert is asked to provide his/her opinion as to the "financial loss" in the matter. A detailed mandate may ask the expert to provide an opinion on...