Association Between the Growth of Accountable Care Organizations and Physician Work Hours and Self-employment.

Importance: The share of the population covered by accountable care organizations (ACOs) is growing, but the association between this increase and physician employment is unknown. Objective: To investigate the association between the growth of ACOs and changes in physician work hours, probability of being self-employed, and probability of working in a hospital. Design, Setting, and Participants: A fixed-effects design was used in this cross-sectional study to compare changes in physician employment in hospital referral regions with high vs low ACO growth. A nationally representative 1% sample of all working US physicians obtained annually from 2011 through 2015 from the American Community Survey (N = 49 582) was included. Data analysis was conducted from March 28, 2017, to April 10, 2018. Main Outcomes and Measures: Physician hours worked per week, probability of being self-employed, and probability of working in a hospital. Results: Of the 49 582 physicians included in the study, 63.5% were men; the mean (SD) age of sampled physicians was 46.01 (11.59) years. In 2011, sampled physicians worked a mean (SD) of 52.2 (16.1) hours per week, 24.43% were self-employed, and 42.03% worked in a hospital. A 10-percentage point increase in ACO enrollment in a hospital referral region was associated with a statistically significant reduction of 0.82 (95% CI, -1.52 to -0.13; P = .02) work hours in men and a decrease of 2% (95% CI, -3.8% to -0.1%; P = .04) in the probability of all physicians being self-employed. The association with self-employment was strongest (-5.0%; 95% CI, -8.7% to -1.4%; P = .006) in physicians aged 50 to 69 years, who were also more likely (4.0%; 95% CI, 1.0% to 6.9%; P = .009) to work in a hospital. Conclusions and Relevance: The growth of ACOs within hospital referral regions appears to be associated with a reduction in hours of work and self-employment among physicians. These results suggest that ACOs may affect physician employment patterns.