In the first of his four-part series for International Tax Review, Bowman (pictured) outlines the best way to select and prepare experts for testimony, addressing some potential problems which may be encountered.
Expert vs material
Expert evidence is opinion evidence on an issue relevant to the proceeding given by a person who is expert in a field in which he or she is testifying.
It differs from material evidence in at least three significant respects:
It is evidence of the opinion of the expert, rather than of a material fact. Evidence of the opinion of a witness who is not an expert is generally inadmissible or, as is more often the case, it is accorded diminished weight unless, of course, the state of a person's mind is a relevant matter of fact.
The traditional view was that an expert may not opine on the very question that the court has to decide. This principle, if it ever existed at all, has never been observed to any degree and it is, as a practical matter, largely unworkable.
Experts are entitled to rely on hearsay evidence in arriving at their opinion. The hearsay evidence on which experts rely is merely the basis on which they form an opinion. It is not, in itself, evidence of the truth of the facts constituting the evidence. Of course, if an expert relies on hearsay evidence that is wrong, the opinion is open to question.
The above are the basic principles relating to expert opinion evidence which is adduced frequently in tax cases in Canada.
Use of experts and potential pitfalls
The lawyer should let the witness draft his or her own statement. This is so self-evident that it need not be stated, but it is a principle that I have seen breached on numerous occasions. However, the lawyer should go over the statement with the witness in detail, suggesting areas that need clarification or expansion. There are some lawyers who will ask for copies of drafts of the expert's statement. I personally question whether they are relevant or producible, but there are some judges who might not agree with that view.
One should not, in instructing an expert witness, set out the conclusion that the lawyer wants reached. If an expert's testimony is prepared with the witness knowing the direction in which the testimony is supposed to be going, the evidence can be weakened or destroyed on cross-examination.
Counsel should not hesitate to refrain from calling a witness at any time up to the point the case is closed. If there are any doubts about the witness' testimony, counsel should err on the side of caution and not call the witness. An ill-considered or injudicious answer from a witness can be far more devastating than not calling the witness at all. If the client can afford it, more experts may be retained and kept in reserve.
Counsel should, in preparing the witness for trial, cross examine the expert extensively, mercilessly and brutally. The witness should be subjected to a far more gruelling cross-examination than any that can be expected from the other side.
It is important to bring out from the witness everything that can be embarrassing. One should leave nothing to chance. I have, more often than I care to remember, seen a witness destroyed in cross examination by being confronted with an embarrassing fact that was never revealed to the lawyer calling that witness.
It is essential to emphasize to the expert the necessity of being and of appearing to be non-partisan. One of the most frequent criticisms that is made of experts is that they become advocates for the side that called them. An expert's apparent lack of objectivity can be fatal. An expert is supposed to be entirely impartial. If the expert witness is so committed to the side that he or she is called to support that an argument between the cross-examiner and the witness ensues, this is doubly fatal.
Frequently in an expert's testimony there is embedded material evidence that counsel wants to put in as part of the factual presentation. One should avoid combining material and opinion evidence into the same testimony of one witness. If both material and opinion evidence is mixed in one witness' testimony, it is confusing and tactically unsound and risks having both types of evidence rejected or at least substantially weakened.
