Specialization among obstetrician/gynecologists. Another dimension of physician supply.

This study uses the Herfindahl index to investigate the specialization patterns of physicians. "Specialization" is defined as the degree to which an individual doctor concentrates his practice into a narrow range of disease categories. This application is the specialization pattern of office-based obstetrician/gynecologists in the United States. Physician's age and solo practice both exhibit a systematic negative effect on specialization. Both the age and type of practice effects reflect the tendency for younger and nonsolo obstetrician/gynecologists to gear relatively more of their practice into birth-related activities. The age effect is consistent with the hypotheses that either: (1) energy and/or skills for treating pregnancy become more scarce with age, or (2) there is a life-cycle pattern in the doctor/patient relationship with pregnancy serving as an entry point. Malpractice concerns may also contribute to this age effect. The nonsolo practitioner effect suggests the efficiency of multiple doctor practices for allocating physicians' time in activities with high hourly variability in demand. The method used to measure specialization can be extended to investigate other specialty categories and important issues regarding the future supply of physicians' services. These include the effects of an aging physician population and proposed changes in physician reimbursement.