Health care expenditures in the United States are continuing to climb faster than the rate of inflation and are projected by the Centers for Medicare and Medicaid Services to exceed 19% of gross domestic product by 2019.1 This trend poses significant threats to the national economy and the competitiveness of American business.2 The impact of expanding health insurance coverage under recently enacted health care reform legislation is estimated to be about $1 trillion, increasing the urgency of finding new approaches to “bend the cost curve.”3 A number of modifications to current payment systems have been proposed to influence the spending behaviors of patients, hospitals, and physicians. However, considerable uncertainty persists regarding the potential impact of various proposals. In short, the answers are not simple, and the unanticipated consequences of various policy options are, well, hard to anticipate.