Office-based medical practices: methods and estimates from the national ambulatory medical care survey.

Objectives: The report uses a multiplicity estimator from a sample of office-based physicians to estimate the number and characteristics of medical practices in the United States. Practice estimates are presented by characteristics of the practice (solo or group, single, or multi-specialty group, size of practice, ownership, location, number of managed care contracts, use of electronic medical records, and use of computerized physician order entry systems).

Methods: Data presented in this report were collected during physician induction interviews for the 2003-04 National Ambulatory Medical Care Survey (NAMCS). The NAMCS is a national probability sample survey of nonfederal physicians who see patients in an office setting in the United States. Radiologists, anesthesiologists, and pathologists-as well as physicians who treat patients solely in hospital, institutional, or occupational settings-are excluded. Sample weights for physician data use information on the number of physicians in the sampled physician's practice to produce annual national estimates of medical practices.

Results: During 2003-04, an average of 311,200 office-based physicians practiced in an estimated 161,200 medical practices in the United States. Medical practice characteristics differed from physician characteristics. Although 35.8 percent of office-based physicians were in solo practice, 69.2 percent of medical practices consisted of solo practitioners. The one-fifth of medical practices with three or more physicians (19.5 percent) contains about one-half of all office-based physicians (52.4 percent). About 8.4 percent of medical practices involved multiple specialties. Fifteen percent of medical practices, consisting of 19.0 percent of physicians, used electronic medical records. Similarly, 6.5 percent of medical practices, consisting of 9.2 percent of physicians, used computerized prescription order entry systems.