Much of the US population resides in areas where ACOs have been established. ACO formation has taken place where it may be easier to meet quality and cost targets. Wider adoption of the ACO model may require tailoring to local context.

This cross-site comparison of the early experience of four provider organizations participating in the Brookings-Dartmouth Accountable Care Organization Collaborative identifies factors that sites perceived as enablers of successful ACO formation and performance. The four pilots varied in size, with between 7,000 and 50,000 attributed patients and 90 to 2,700 participating physicians. The sites had varying degrees of experience with performance-based payments; however, all formed collaborative new relationships with payers and created shared savings agreements linked to performance on quality measures. Each organization devoted major efforts to physician engagement. Policy makers now need to consider how to support and provide incentives for the successful formation of multipayer ACOs, and how to align privatesector and CMS performance measures. Linking providers to learning networks where payers and providers can address common technical issues could help. These sites' transitions to the new payment model constitutes an ongoing journey that will require continual adaptation in the structure of contracts and organizational attributes. I nterest in accountable care organizations (ACOs), a payment model designed to improve quality while reducing costs, is accelerating. Section 3022 of the Affordable Care Act established the Medicare Shared Savings Program. Draft regulations initially proposed were sharply criticized, but in the final rule, the Centers for Medicare and Medicaid Services (CMS) addressed many key stakeholders' concerns. As of now, a total of 116 organizations are participating in that program. 1The Center for Medicare and Medicaid Innovation, a newly created center within CMS, has also established several complementary programs. These include the Advance Payment Initiative 2 to test approaches for providers with limited resources, and the Pioneer ACO Program, 3 designed for providers whose ability to embrace the ACO model is far more advanced. The private sector, too, has moved forward to create a substantial number of commercial ACOs, 4 and several learning networks have emerged to support providers and payers.Despite the extent of ongoing ACO activity in the public and private sectors, there is limited evidence from the field about what factors may contribute to successful progress toward ACO formation. Although some studies have described early results of ACO or ACO-like implementation, 5,6 little is known about the early phases of ACO development and formation. Our research aimed to do the following: document approaches to developing ACO organizational structures and payer agreements; identify factors that may facilitate ACO formation; and analyze the potential policy implications of these emerging ACO arrangements.

Context:It is widely hoped that accountable care organizations (ACOs) will improve health care quality and reduce costs by fostering integration among diverse provider groups. But how do implementers actually envision integration, and what will integration mean in terms of managing the many social identities that ACOs bring together?Methods: Using the lens of the social identity approach, this qualitative study examined how four nascent ACOs engaged with the concept of integration. During multiday site visits, we conducted interviews (114 managers and physicians), observations, and document reviews. Findings:In no case was the ACO interpreted as a new, overarching entity uniting disparate groups; rather, each site offered a unique interpretation that flowed from its existing strategies for social-identity management: An independent practice association preserved members' cherished value of autonomy by emphasizing coordination, not "integration"; a medical group promoted integration within its employed core, but not with affiliates; a hospital, engaging community physicians who mistrusted integrated systems, reimagined integration as an equal partnership; an integrated delivery system advanced its careful journey towards intergroup consensus by presenting the ACO as a cultural, not structural, change.

This study illuminates and explains variation in the way different organisations engage physicians, and offers a theoretical basis for selecting engagement strategies.