Comparative effectiveness research: evidence-based medicine meets health care reform in the USA.

Rationale Comparative effectiveness research (CER) is the study of two or more approaches to a health problem to determine which one results in better health outcomes. It is viewed by some in the USA as a promising strategy for health care reform. Aims and Objectives In this paper, nascent US CER policy will be described and analysed in order to determine its similarities and differences with EBM and its chances of success. Methods Document review and process tracing Results CER shares the logic of policies promoting evidence-based medicine, but invites greater methodological flexibility to ensure external validity across a range of health care topics. Conclusions This may narrow the inferential distance from knowledge to action, but efforts to change the US health care system through CER will face familiar epistemological quandaries and 'patient-centred' politics on the left and right.