What is the case law on the admissibility of expert evidence in medical malpractice cases?

[21] The leading case on the admissibility of expert evidence is The Queen v. Mohan, [1994] 2 S.C.R. 9, 166 N.R. 245, 71 O.A.C. 241, 114 D.L.R. (4th) 419, 89 C.C.C. (3d) 402, 29 C.R. (4th) 243, 1994 CanLII 80, [1994] S.C.J. No. 36, 1994 Cars­well­Ont 6. The Queen v. Mohan held that there are four criteria that must be applied for the admission of expert evidence. Should any of these four criteria not be satisfied, the proposed evidence is not admissible. The threshold criterion is whether the proposed evidence is relevant.

[22] According to The Queen v. Mohan, relevance has at least two aspects. First, the evidence must be logically relevant in that it is so related to a fact in issue that it tends to establish that fact. Second, the court must engage in a “cost-benefit” analysis. Specifically, the court must decide whether the benefit that would flow from the admission of the evidence — notwithstanding its logical relevance — would be outweighed by its cost. By “cost” the court meant any prejudicial impact that might result from the admission of that evidence. For example, if the admission of the evidence would require such an inordinate amount of time, an amount of time that is not commensurate with the benefit to be obtained, the court should not allow the evidence to be adduced; see page 21 [S.C.R.].