In order to support a claim of medical malpractice, expert testimony will most likely be necessary to show (a) the applicable standard of care; (b) the breach of the standard of care; and (c) that the breach in the standard of care caused injury to the plaintiff.
Some of the criteria for determining whether a witness can be considered an expert witness are:
(a) relationship of the professional specialty of the witness to the medical problem and type of treatment administered in the case;
(b) whether the witness devotes a substantial amount of time to the practice of medicine, teaching or university based research in the areas giving rise to the type of treatment administered in the case;
(c) whether the witness is licensed in the same area as the the defendant doctor;
(d) with a non-specialist defendant, whether the witness is sufficiently familiar with the standard of care at issue.
Expert testimony on the issue of causation and injury to the plaintiff does not need to be from a doctor practicing in the same school of medicine as the defendant.