Building on the American Recovery and Reinvestment Act of 2009, health reform legislation would develop an infrastructure for the ongoing generation and dissemination of information on the comparative effectiveness, where "comparative effectiveness" has been defined as the study of methods to prevent, diagnoses, treat, and monitor A clinical condition or improve delivery of care to assist consumers, clinicians, purchasers, and policy makers to make informed decisions to improve health care at both individual and population levels. The issue brief explores the concept and describes areas of controversy that need to be addressed to make comparative effectiveness research successful.