Comparative effectiveness: asking the right questions, choosing the right method.

The Medicare Prescription Drug, Improvement, and Modernization Act (MMA) of 2003 has placed renewed focus on assessing the comparative effectiveness of various therapeutic options. Unfortunately, all of the evidence needed to fully assess these options is rarely available to drug formulary decisionmakers. Comparative randomized trials frequently fail to find differences when there indeed are some, while decision-modeling approaches are more likely to identify differences where there are none. We consider the consequences of these strategies. This paper proposes a framework for using different methods to assess available evidence. We contend that choosing the appropriate method can occur only when there are clear policy goals.