When it is well conducted, a randomized clinical provides the strongest evidence available for evaluating the comparative effectiveness of the interventions tested. Over the last two generations, we have learned much about various devices for strengthening them and about methods of avoiding between in their design, execution, analysis, and reporting. In a trial, we seek evidence for a causal link between treatment and observed outcomes. Becaues the controlled trial depends on an argument based on exculsion (i.e., no other causes or differences affected the experimental groups), we strengthen its inference by taking steps to exclude any such differences.
This article discusses a number of issues that deserve consideration: problems of multiplicity and generalizability, devices for strengthening trials, issues of power and sample size, the relationship between study design and reported gains, when to undertake a trial, the role of collaborative trials, and ways to make trials more feasible in clinical settings.