In R v. Abbey1, Dickson J. held:
Witnesses testify as to facts. The judge or jury draws inferences from facts. With respect to matters calling for special knowledge, an expert in the field may draw inferences and state his opinion. An expert’s function is precisely this: to provide the judge and jury with the ready-made inference which the judge and jury, due to the technical nature of the facts, are unable to formulate. An expert’s opinion is admissible to furnish the court with scientific information, which is likely to be outside the experience and knowledge of a judge or jury.
As science and technology have become more complex, the role of the expert witness has become increasingly more important. The selection and preparation of the expert witness has been and will prove to be at the cornerstone of much successful litigation.
The Ikarian Reefer
The British decision commonly referred to as The Ikarian Reefer2, a 1993 decision of Justice Cresswell, has been referred to in a number of Canadian decisions as providing certain guidelines for expert evidence and as setting out certain duties of the expert witness.
The first two duties referred to by Justice Cresswell are as follows:
- Expert evidence presented to the court should be, and should be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of litigation; and
- An expert witness should provide independent assistance to the court by way of objective, unbiased opinion in relation to matters within his expertise.
The courts tend to be wary of an expert who assumes the role of an advocate or advances a self-serving viewpoint. Expert testimony that appears objective and well-balanced is likely to be accorded more weight and is more likely to be relied upon by the trier of fact.
1 2 S.C.R. 24
2The Ikarian Reefer  2 Lloyds Rep. 68 (Comm. Ct. Q.B. Div.) (full style: National Justice Compania S.A. v. Prudential Assurance Co. Ltd.)
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