The First Decade of ACO Model Evaluations in the Medicare Program: A Systematic Review

Health care providers participating in five accountable care organization (ACO) models designed, implemented, and evaluated by the Innovation Center at the Centers for Medicare & Medicaid Services have cared for almost six million fee-for-service Medicare patients over the past decade. This systematic review summarizes the features and performance of these ACO models, capturing five major themes arising from their evaluation reports: spending performance by ACO organization type; the role of management companies in ACO structure and performance; financial risk and ACO participation; clinician incentives, waivers, and payment mechanisms; and patient engagement with ACOs. In difference-in-differences analyses, these 214 ACOs lowered spending by an estimated $2.8 billion, or $316.9 million after accounting for shared savings payouts derived from benchmarks, with no evident decrements in quality of care. ACOs’ challenge in ongoing and future ACO models is to apply their accrued experience to reduce spending and improve quality within a fee-for-service payment system.