The standard of care in medical malpractice law varies by the locality from which different states draw their customary care practices. The customary care standard was historically limited to physicians practicing in close proximity to each other. Currently, only six states maintain a version of the “locality rule,” in which a physician is judged by the standard of care in his or her particular locality, requiring a defendant-physician to provide the same degree of skill and care that is required of a physician practicing in the same or a similar community.
The locality rule was created to protect physicians in rural areas from being held to a higher legal standard when they did not necessarily have access to the same level of training or technology as physicians in urban areas. However, as stated in Hall v. Hilbun:
We would have to put our heads in the sand to ignore the ‘nationalization’ of medical education and training. Medical school admission standards are similar across the country. … Differences and changes in these areas occur temporally, not geographically…. Common sense and experience inform us that the laws of medicine do not vary from state to state in anything like the manner our public law does.
Generally, the customary standard provides a safe haven for physicians who align themselves with the status quo regardless of whether or not this affiliation reflects the latest medical information. Alternatively, an individual physician could comply with an evidence-based standard that is inconsistent with local custom. Locality rule jurisdictions also create serious obstacles for patients who seek to pursue medical negligence claims because it may be difficult to engage an expert-witness physician from a community to testify against another physician in the same community.
Today, most jurisdictions require physicians to provide patients with care comparable to the care the patient would receive anywhere in the United States. The national standard of care requires a doctor to use the degree of skill and care of a reasonably competent practitioner in his field under same or similar circumstances, regardless of locality.  In jurisdictions that use a national standard of care, physicians benefit from being held accountable to a more expansive standard because they no longer need to choose between following local practice customs and national standards. Patients likely benefit from a national standard of care because meritorious lawsuits might not be brought in jurisdictions that adhere to locality standards.
Even though the traditional locality rule may soon be an anachronism, national standard jurisdictions are not exempt from significant, geographical irregularities. The same problems that plague healthcare providers as a result of the absence of explicit care standards are evident in the legal field where at least one quarter of states reject conclusive deference to medical custom and nearly half of all jurisdictions employ some degree of reasonableness to their medical negligence calculus. Several jurisdictions have relaxed the custom-based standard by recognizing “two schools of thought” or “respectable minority” rules, which preclude liability if the defendant can show that physicians are divided over the appropriate treatment course and the defendant picked one of the acceptable options. Some courts require the plaintiff to show that a “considerable number” of physicians have adopted the defendant's choice, while others simply require that those in the minority be regarded as “respectable” by their peers; still others mandate both requirements. Other jurisdictions reject the “respectable minority” defense, reasoning that the propriety of taking a particular approach cannot be ascertained by determining whether other physicians follow that practice.
Additionally, some courts allow “honest error in judgment” jury instructions, which explain that physicians who make reasonable treatment decisions should not be held liable for bad outcomes. Other courts have decided that the simplest way to avoid introducing subjective considerations where objective negligence criteria should rule is to eliminate the “honest error” instructions. Finally, some courts allow jury instructions stating that the physician must use her “best judgment” by relying on any superior knowledge or skill that she possesses, which might dictate a higher standard of care than that of the average reasonable practitioner.
Each of these jurisdictional modifications exists because courts recognize the necessity of reconciling customary care and medical evidence. However, the absence of explicit legal standards fails to provide physicians with notice of which rules apply and often results in a courtroom battle. Professor Havighurst of Duke School of law aptly described the dilemma:
“[a]s malpractice law is currently administered, its requirements are extraordinarily vague and unpredictable. . . . Given the considerable vagueness of the standards it imposes so rigorously on physicians, the tort system would probably not survive scrutiny under constitutional norms of due process if it operated as a public regulatory program de jure as well as de facto.”
These jurisdictional variations in custom-based legal standards highlight fundamental problems with existing medical malpractice doctrine: the law begins with the premise that the physician should act according to prevailing practices, but courts hit a stumbling block when they acknowledge that medical knowledge rapidly advances over time. It logically follows that the law should require reasonable physicians to incorporate newly acquired information into their decision-making, however, this proposition is at odds with a system based in customary care.
 The Locality Rule and the Physician’s Dilemma - Local Medical Practices vs. the National Standard of Care, Lewis, et al., JAMA. 2007;297(23):2633-2637.  E. Lee Schlender, Malpractice and the Idaho Locality Rule: Stuck in the Nineteenth Century, 44 Idaho L. Rev. 361, 365-70 (2008).  466 So. 2d 856 (Miss. 1985).  Id. at 870.  Id.  Philip G. Peters, Jr., Quiet Demise of Deference to Custom: Malpractice Law at the Millennium, 57 Wash. & Lee L. Rev. 163, 172-87 (2000).  Id.  Id.  Haase v. Garfinkel, 418 S.W.2d 108, 114 (Mo. 1967); Furey v. Thomas Jefferson Univ. Hosp., 472 A.2d 1083, 1089 (Pa. Super. Ct. 1984).  Anna B. Laakmann, When Should Physicians Be Liable for Innovation?, 36 Cardozo L. Rev. 913, 918 (2015).  See, e.g., State Bd. of Med. Exam'rs v. McCroskey, 880 P.2d 1188, 1194-95 (Colo. 1994).  See, e.g., Capolino v. N.Y.C. Health & Hosps. Corp., 605 N.Y.S.2d 87, 88 (App. Div. 1993).  Currie v. United States, 644 F. Supp. 1074 (M.D.N.C. 1986), aff'd, 836 F.2d 209 (4th Cir. 1987).  See Joseph H. King, Jr., Reconciling the Exercise of Judgment and the Objective Standard of Care in Medical Malpractice, 52 Okla. L. Rev. 49, 50 (1999).  Clark C. Havighurst, Practice Guidelines as Legal Standards Governing Physician Liability, Law & Contemp. Probs., Spring 1991, at 96.