The analysis of current estimates of the number of physicians practicing in the United States by Staiger and colleagues1 in this issue of JAMA touches on a topic that is both arcane and central to policy debates. The arcane part is how physicians are counted; the policy part is how their contributions to the economy and to social needs are estimated.
The study by Staiger et al1 examines a central source of data on the supply of physicians, the American Medical Association (AMA) Physician Masterfile. This is a longstanding inventory of the supply of all physicians, alive and dead, practicing medicine or not. Its origins trace back to 1906 when the AMA attempted to identify all practicing physicians in the United States, members and nonmembers.2 The data file became widely accepted as the authoritative source of information about the number and location of physicians to the point that in 1966, the National Committee on Vital and Health Statistics, in a report entitled “United States Statistics on Medical Economics,” took note of the value of the data file as a reliable source for information on the “geographic location, age, sex and specialty” of physicians, but also noted that the data could be improved to better reflect the volume of patient care the physician provided.3 In 1968, the AMA Center for Health Services Research and Development revised its data collection processes and its method of classifying physicians. The file has since undergone various efforts to improve its quality over the years because it also is a source of revenue for the AMA,4 as well as reference data for public policy deliberations.