What is the test for determining whether a physician was negligent or simply exercised an error in judgment?

Whether or not the physician was negligent or simply exercised an error in judgment will be determined on a case-by-case basis having regard to the particular facts in each case: A diagnosis is above all, an exercise of the physician’s judgment based on his training, experience and perhaps, intuition. It is trite to say that a physician is not liable for injuries flowing from errors of judgment (as opposed to actual negligence). The real difficulty lies in determining whether injurious behaviour by a physician was negligent or merely an error in judgment and it is the facts in each case which would determine the answer to this crucial question. See: Dean v. York County Hospital et al [1979] O.J. No. 348. No retrospective judgement or hindsight