La preuve à l'appui de l'expertise doit être établie devant la Cour, car à défaut, la valeur probante de l'expertise s’en trouvera affaiblie

R. v. Collins, 2001 CanLII 24124 (ON CA)

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[46]         While it is conceivable that the latter part of this instruction could have some valid application to a particular fact situation, it is incorrect as a general principle of law and should not be routinely given. There is no basis at law for differentiating between Crown and defence expert opinion evidence when it comes to assessing the evidentiary foundation for the opinion. In either case, the more the expert relies on facts not proved in evidence, the less weight the jury may attribute to the opinion. The corollary is also true: the more the expert fails to consider relevant facts, the less weight the jury may attribute to the opinion. These principles apply in the same way whether the expert opinion favours the Crown or the defence. See R. v. Abbey, supra; R. v. Lavallee, 1990 CanLII 95 (SCC), [1990] 1 S.C.R. 852; and more recently, R. v. Charlebois, 2000 SCC 53 (CanLII), [2000]  2 S.C.R. 674 at para. 22 where the court reviewed the correctness of jury instructions in relation to a defence expert and did so solely in terms of these principles.