Comparison of physician workforce estimates and supply projections.

CONTEXT Estimates of physician supply in the United States have been based on data that may overestimate the number of older physicians in the workforce. OBJECTIVE To compare physician workforce estimates and supply projections using the American Medical Association Physician Masterfile (Masterfile) data with estimates and projections using data from the US Census Bureau Current Population Survey (CPS). DESIGN, SETTING, AND PARTICIPANTS Parallel retrospective cohort analyses of employment trends of the number of active physicians by age and sex using annual data from the Masterfile and the CPS between 1979 and 2008. Recent workforce trends were used to project future physician supply by age. MAIN OUTCOME MEASURE Annual number of physicians working at least 20 hours per week in 10-year age categories. RESULTS In an average year in the sample period, the CPS estimated 67,000 (10%) fewer active physicians than did the Masterfile (95% confidence interval [CI], 57,000-78,000; P < .001), almost entirely due to fewer active physicians aged 55 years or older. The CPS estimated more young physicians (ages 25-34 years) than did the Masterfile, with the difference increasing to an average of 17,000 (12%) during the final 15 years (95% CI, 13,000-22,000; P < .001). The CPS estimates of more young physicians were consistent with historical growth observed in the number of first-year residents, and the CPS estimates of fewer older physicians were consistent with lower Medicare billing by older physicians. Projections based on both the CPS and the Masterfile data indicate that the number of active physicians will increase by approximately 20% between 2005 and 2020. However, projections for 2020 using CPS data estimate nearly 100,000 (9%) fewer active physicians than projections using the Masterfile data (957,000 vs 1,050,000), and estimate that a smaller proportion of active physicians will be 65 years or older (9% vs 18%). The increasing proportion of female physicians had little effect on physician supply projections because, unlike male physicians, female physicians were found to maintain their work activity after age 55 years. CONCLUSION Compared with the Masterfile data, estimates using the CPS data found more young physicians entering the workforce and fewer older physicians remaining active, resulting in estimates of a smaller and younger physician workforce now and in the future.