An expert witness must establish a standard for medical care and give an opinion on whether the defendant’s conduct met this standard. The standard must at once be general to all practitioners and specific to the individual plaintiff’s circumstances. Ideally, it should be supported by uncontroverted scholarly literature. While it need not prescribe a single course of action, it must either (for the plaintiff) proscribe the defendant’s conduct or (for the defense) endorse the defendant’s conduct as an acceptable alternative.

These standards ignore the conflict between actual medical practice and legal expectations. The courts expect that medicine, as a learned, science- based discipline, will have articulated standards for practice. While recognizing the art in medicine, the law assumes that the science of medicine will be sufficiently formalized that the regions of art will be readily identifiable. Rather than face the core problem of inadequately defined practice standards, the courts allow experts to step into this void with standards tailored to serve the desired ends of the lawyer engaging the expert.