Individual studies rarely provide definitive answers to clinical effectiveness questions (Cook et al., 1997). If it is conducted properly, a systematic review should make obvious the gap between what is known about the effectiveness of a particular service and what clinicians and patients want to know (Helfand, 2005). As such, systematic reviews are also critical to the development of an agenda for further primary research because they reveal where the evidence is insufficient and new information is needed (Neumann, 2006). Without systematic reviews, researchers may miss promising leads or pursue questions that have already been answered (Mulrow et al., 1997). In addition, systematic reviews provide an essential bridge between the body of research evidence and the development of clinical guidance.

This section briefly describes the variety of contexts in which key U.S. organizations produce or use systematic reviews (Table 4-1). The ultimate purposes of systematic reviews vary and include health coverage decisions, practice guidelines, regulatory approval of new pharmaceuticals or medical devices, clinical research or program planning. Within the federal government, the users include the Agency for Healthcare Research and Quality (AHRQ), the Centers for Medicare & Medicaid Services (CMS), the Medicare Evidence Development and Coverage Advisory Committee (MedCAC), the Centers for Disease Control and Prevention (CDC), the U.S. Food and Drug Administration (FDA), the Substance Abuse and Mental Health Administration (SAMHSA), the U.S. Preventive Services Task Force (USPSTF), and the Veterans Health Administration (VHA).

AHRQ plays a lead role in producing systematic reviews through its program of Evidence-based Practice Centers (EPCs) as a part of its Effective Health Care Program. EPCs produce systematic reviews for professional medical societies and several federal agencies, including CMS and the National Institutes of Health (NIH) Consensus Development Conferences, as well as a variety of other public and private requestors, such as the USPSTF and the American Heart Association. The reviews cover a broad range of topics, including the effectiveness and safety of health care interventions, emergency preparedness, research methods, and approaches to improving the quality and delivery of health care.¹ The AHRQ Effective Health Care Program produces comparative effectiveness studies on surgical procedures, medical devices, and medical therapies in 10 priority areas (Slutsky, 2007).

The CDC conducts or sponsors systematic effectiveness reviews to evaluate and make recommendations on population-based and public