What is the objective test for determining whether a surgeon breached their duty of disclosure by failing to disclose to a patient?

37 The question of which test is the correct one was discussed at length in Reibl v. Hughes. At 898-900 S.C.R., Laskin C.J.C. said this: I think it is the safer course on the issue of causation to consider objectively how far the balance in the risks of surgery or no surgery is in favour of undergoing surgery. The failure of proper disclosure pro and con becomes therefore very material. And so too are any special considerations affecting the particular patient. For example, the patient may have asked specific questions which were either brushed aside or were not fully answered or were answered wrongly. In the present case, the anticipation of a full pension would be a special consideration, and, while it would have to be viewed objectively, it emerges from the patient's particular circumstances. So too, other aspects of the objective standard would have to be geared to what the average prudent person, the reasonable person in the patient's particular position, would agree to or not agree to, if all material and special risks of going ahead with the surgery or foregoing it were made known to him. Far from making the patient's own testimony irrelevant, it is essential to his case that he put his own position forward. The adoption of an objective standard does not mean that the issue of causation is completely in the hands of the surgeon. Merely because medical evidence establishes the reasonableness of a recommended operation does not mean that a reasonable person in the patient's position would necessarily agree to it, if proper disclosure had been made of the risks attendant upon it, balanced by those against it. The patient's particular situation and the degree to which the risks of surgery or no surgery are balanced would reduce the force, on an objective appraisal, of the surgeon's recommendation. Admittedly, if the risk of foregoing the surgery would be considerably graver to a patient than the risks attendant upon it, the objective standard would favour exoneration of the surgeon who has not made the required disclosure. Since liability rests only in negligence, in a failure to disclose material risks, the issue of causation would be in the patient's hands on a subjective test, and would, if his evidence was accepted, result inevitably in liability unless, of course, there was a finding that there was no breach of the duty of disclosure. In my view, therefore, the objective standard is the preferable one on the issue of causation. In saying that the test is based on the decision that a reasonable person in the patient's position would have made, I should make it clear that the patient's particular concerns must also be reasonably based; otherwise, there would be more subjectivity than would be warranted under an objective test. Thus, for example, fears which are not related to the material risks which should have been but were not disclosed would not be causative factors. However, economic considerations could reasonably go to causation where, for example, the loss of an eye as a result of non-disclosure of a material risk brings about the loss of a job for which good eyesight is required. In short, although account must be taken of a patient's particular position, a position which will vary with the patient, it must be objectively assessed in terms of reasonableness.