Growth of accountable care organizations (ACOs) could affect physician employment patterns, due to reduced work hours and a decreased probability of self-employment, according to a study published in JAMA Network Open.

This cross-sectional study sought to investigate the association between growing ACOs and changes in physician work variables by looking at specific outcomes, including the number of hours worked per week and the probability of being self-employed vs the probability of working in a hospital. These outcomes were compared in hospital referral regions with high vs low ACO growth.

Data on 49,582 working physicians were retrieved from the nationally representative American Community Survey between 2011 and 2015. The number of weekly hours a physician worked was self-reported, as was the industry of their employer or self-employment status. Basic demographic information was collected and showed the study sample was composed of 63.5% men; the participants’ mean age was 46 years. ACO enrollment rates during the defined time period were calculated as the percentage of the population covered under ACO contract according to hospital referral region.

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Study results showed that between 2011 and 2015, ACO enrollment grew from 11% to 38% in the top hospital referral regions experiencing rapid ACO growth. Mean ACO enrollment across all regions grew from 1.14% in 2011 to 9.13% in 2015. In 2011, physicians worked a mean of 52.2 hours a week; 24.43% were self-employed, and 42.03% worked in a hospital. By 2015, mean physician work hours decreased to 51.9 hours a week, and a shift from self-employment to hospital employment was reported (20.3% were self-employed and 46.6% worked in hospitals).

The study used multiple regression analysis to estimate an association between a 10% increase in ACO enrollment and physician employment variables. An overall reduction of 0.62 work hours per week (95% CI, -1.31 to 0.07 hours; P =.08) was associated with a 10% increase in ACO enrollment, but only among male physicians were the changes in hours statistically significant (0.82 hours; 95% CI, -1.52 to -0.13 hours; P =.02). The probability of being self-employed saw a 2% decrease overall associated with a 10% increase in ACO enrollment. The strongest association to ACO growth was a 5% reduction in self-employment among physicians aged 50 to 69 years (95% CI, -8.7% to -1.4%; P =.006). This group was also 4% more likely to work in a hospital (95% CI, 1.0% to -6.9%; P =.009).

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Limitations of the study included a lack of data identifying physician specialties and whether the participating physicians worked directly for an ACO. Another limit of the study was the observational nature defining the association between employment variables and ACO growth: The direction of causation may be the reverse of what the authors identified, in which ACOs arise in response to changing physician preferences.

Study authors conclude that well-performing ACOs make more efficient use of physician time by shifting tasks to other hospital team members. In addition, ACO growth may be responsible for stimulating a trend of physicians seeking employment in hospitals and consequently decreasing self-employment.


Mahajan A, Skinner L, Auerbach DI, Buerhaus PI, Staiger DO. Association between the growth of accountable care organizations and physician work hours and self-employment [published online July 27, 2018]. JAMA Netw Open. doi: 10.1001/jamanetworkopen.2018.0876.