A simple random sample of 3,544 physicians in private practice was surveyed regarding experience, specialty, training, and volume of visits. The responses from 2,833 were tabulated for the United States and regions of the country, for specialty and type of practice groupings, and metropolitan and nonmetropolitan locations of practice.
Theodore CN, Sutter GE. A Report on the First Periodic Survey of Physicians. JAMA. 1967;202(6):516-524. doi:10.1001/jama.1967.03130190122019