'Marginal medicine': targeting comparative effectiveness research to reduce waste.

Many policymakers believe that comparative effectiveness research will reduce "waste" in the U.S. health care system by providing guidance on what health care options work best for different patients. How such research will produce findings that identify waste has not been clearly elucidated. This paper presents a conceptual framework for different evidentiary categories of what we call "marginal medicine." This framework could help clinicians, researchers, and policymakers align the results of comparative effectiveness research with efforts to identify opportunities to improve the value of health care services.