What is the test for negligence in medical malpractice cases?

There is a distinction between an error in judgment and an act of unskilfulness or carelessness or due to lack of knowledge. This distinction was stated in Rann v. Twitchell (1909), 82 Vt. 79 at 84, 71 A. 1045, thus: "He is not to be judged by the result, nor is he to be held liable for an error of judgment. His negligence is to be determined by reference to the pertinent facts existing at the time of his examination and treatment, of which he knew, or in the exercise of due care, should have known. It may consist in a failure to apply the proper remedy upon a correct determination of existing physical conditions, or it may precede that and result from a failure properly to inform himself of these conditions. If the latter, then it must appear that he had a reasonable opportunity for examination and that the true physical conditions were so apparent that they could have been ascertained by the exercise of the required degree of care and skill. For, if a determination of these physical facts resolves itself into a question of judgment merely, he cannot be held liable for his error."