Antitrust and Accountable Care Organizations: Observations for the Physician Market.

The creation of Accountable Care Organizations (ACOs) under the Medicare Shared Savings Program has generated antitrust concerns. Utilizing a framework developed by the antitrust authorities for analyzing provider concentration for potential ACO participants, we examine the market for physician services, with a focus on the share of practices that could potentially be subject to antitrust scrutiny. Our findings suggest that while most physician practices would fall below the threshold that could raise anticompetitive concerns, this varies considerably by market and specialty. Furthermore, we find that the largest physician practice in most markets potentially remains at risk for antitrust review under the existing criteria.