What is the purpose of leading the evidence in a mental health case?

In my opinion, the trial judge misconstrued the purpose of leading the evidence as to the basis on which the psychiatrists reached their opinions. The opinions, as Ritchie J. said in Phillion v. The Queen (1977), 1977 CanLII 23 (SCC), 33 C.C.C. (2d) 535, 74 D.L.R. (3d) 136, [1978] 1 S.C.R. 18, were admissible because they were relevant to an issue before the trial judge in the proceedings but the secondhand evidence upon which they were based was not admissible in proof of the truth but rather as indicating the basis upon which the opinions were formed in accordance with recognized professional procedures.

That was also the view expressed in Wilband v. The Queen, supra, where Fauteux J. said at p. 11 C.C.C, p. 297 W.W.R.: The value of a psychiatrist's opinion may be affected to the extent to which it may rest on second-hand source material; but that goes to weight and not to the receivability in evidence of the opinion, which opinion is no evidence of the truth of the information but evidence of the opinion formed on the basis of that information.