Once the plaintiff has established that there was a legal relationship with the physician defendant, the plaintiff must establish the appropriate standard of care. In theory, establishing the standard of care and establishing the breach of that standard are legally separate. In reality, unless there is a factual question about what the defendant did, the proof of the standard of care also proves the defendant’s breach. For example, assume that the defendant admits that she did not counsel the patient about prenatal testing for a genetic disease. If the patient can establish that the standard of care was to offer this testing, the defendant breached the standard. If, however, the physician claims to have done the counseling, the patient will have to prove both that counseling was the standard of care and that the physician did not do the counseling.

The most common legal definition of standard of care is how similarly qualified practitioners would have managed the patient’s care under the same or similar circumstances. This is not simply what the majority of practitioners would have done. The courts recognize the respectable minority rule. This rule allows the practitioner to show that although the course of therapy followed was not the same as other practitioners would have followed, it is one that is accepted by a respectable minority of practitioners (respectable is used in both senses). The jury is not bound to accept the majority standard of care. Jurors may decide that a minority standard is the proper standard and that a physician following the majority standard was negligent.

The courts have delegated the setting of professional standards to members of the various professions. This is in contrast to the standards for nonprofessional skills, such as driving a car. The legislature establishes the rules of the road, and a lay juror is deemed capable of determining when they have been violated. In contrast, legislatures do not adopt detailed standards for professional practice. Medical practice standards are drawn from the customs and behavior of the members of the profession. If the profession has developed documents that reflect a consensus on how the profession is to be practiced, these documents will set the standard for judging individual transgressions.

In most medical malpractice cases, both the standard of care and its breach are established through the testimony of expert witnesses. There are situations in which the plaintiff may be able to establish the standard of care and breach without an expert witness.