As a consequence of this change, juries may hear jury instructions describing the standard of care in terms of reasonability, rather than compliance with custom, and judges may permit plaintiffs to reach a jury without proving that the defendant failed to do what most physicians do. . . . Nevertheless, it is certainly possible that some of the reasonable- physician states ultimately will conclude that reasonable physician behavior is defined by customary practices. In addition, several others states, like Pennsylvania, Ohio, Arizona, Michigan, and California, have some authority favoring a reasonable-physician standard and could easily join the others. . . . Even in jurisdictions that continue to endorse a customary standard of care, courts often give experts a considerable amount of latitude in the phrasing of their testimony. They do not insist that these experts prove that a prevailing custom existed and that the defendant deviated from it.
Similar examples exist in many other states purportedly retaining a customary standard of care.
Although some courts have been stricter, a fair amount of fudging appears to be taking place. In the courthouse, plaintiffs often reach juries without proof of deviation from customary norms. These cases warn us not to overestimate the extent to which custom, rather than reasonability, provides the actual standard of care in those states that ostensibly endorse a customary standard of care. When the defendant and her experts disagree with the plaintiff's experts, the jury chooses between them, just as it does in other complex, expert-aided torts actions, such as those involving airplane design or architectural negligence. . . . The twentieth century judicial retreat from reliance on local customs in favor of a standard based either on national standards or the standards of similar localities may have accentuated this tendency toward loose application of the custom-based standard of care.