A study of a large Pioneer ACO found substantial physician and patient turnover over a three-year contract period.
The study, published in Health Affairs, examines organizational and Medicare data from 2012 to 2014 on Somerville, Mass.-based Partners ACO, part of Boston-based Partners HealthCare.
Researchers found only a small portion of participating physicians' patients were attributed to the ACO, and physicians joined and left the ACO regularly throughout the contract, bringing patients with them.
"These findings may help explain the muted financial impact ACOs have had overall, and they raise the possibility of future gaming on the part of ACOs to artificially control spending," the authors wrote.
Here are their two main findings.
1. Less than 5 percent of a typical patient panel was assigned to the ACO. Over the three years studied, a total of 748 physicians participated in the ACO. However, not all of these physicians actually had patients attributed to the ACO while they were signed on to participate. In fact, 87 physicians did not have an attributed beneficiary. For the 661 physicians who did have attributed beneficiaries, the numbers were limited. The average physician had 70 patients attributed to the ACO, though the average patient panel during the study period was 1,700 patients.
"This limited ACO penetration at the physician level could mitigate the ACO's potential to achieve its financial targets, at least for any effects mediated through physician behavior," the authors wrote.
Because each physician had few patients in the ACO, the researchers also found the distribution of the sickest beneficiaries — those with annual Medicare spending north of $81,461 in 2012 — was skewed, meaning a small number of physicians took care of all the sickest patients.
2. Physician turnover generated patient turnover. Only 52 percent of physicians remained affiliated with the ACO for the full three-year contract, according to the study. Throughout the contract period, 41 percent of physicians joined the ACO and 18 percent left, and patients often followed their physicians. The authors found 90 percent of patients left the ACO if their physician left. Similarly, the ACO mostly grew by new physicians joining the organization, rather than by participating physicians adding more patients to the program. The researchers determined half of patient growth over the study period could be attributed to physicians joining the ACO.
The authors suggest that these levels of turnover not only could dilute the ACO's overall financial and quality impact, but could also be gamed to make ACO performance appear more favorably.
"Because of the central role of physicians in linking beneficiaries with ACOs, however, changes in an ACO's affiliated physicians also could represent intentional efforts by the ACOs to influence the composition of the attributed patient population, such as removing subpopulations having less favorable health risk profiles by dropping particular physicians, or vice versa," the authors wrote.
They conclude with the suggestion that health systems reconsider the role of physicians within the ACO and the dependency on physician-level efforts to ensure ACO success.
"In such diffuse situations, system-level approaches might represent a better strategy, particularly those that directly engage beneficiaries through system-level interventions and augment physician efforts, instead of relying on individual physicians' changing their practice patterns for ACO beneficiaries, although such programs could require more effort to develop," the authors wrote.
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