Most phase III clinical trials today are explanatory. Because explanatory, or efficacy, trials test hypotheses under “ideal” conditions, they are not well suited to providing guidance on decisions made in most clinical care contexts. Pragmatic trials, which test hypotheses under “usual” conditions, are often better suited to this task. Yet, pragmatic, or effectiveness, trials are infrequently carried out. This mismatch between the design of clinical trials and the needs of health care professionals is frustrating for everyone involved, and explains some (...) of the challenges inherent in attempts to enhance knowledge translation and encourage evidence-based practice. The situation is more than simply frustrating, however; it is potentially unethical. Clinical trials must be socially valuable in order to (1) warrant the risks they impose on human research subjects and (2) fairly and efficiently assess new clinical interventions. Most bioethicists would agree that trials that have no social value, for instance, because their results do not have the potential to advance clinical care, should not be performed. What is less widely appreciated is that given limited research resources, trials that are more socially valuable should be preferred to trials that are less socially valuable when all else is equal. With respect to clinical trial design, I argue that while explanatory trials often have some social value, many have less social value than their pragmatic counterparts. On the basis of this general ethical assessment, I provide a preliminary defense of the position that clinical researchers should aim to conduct pragmatic trials, that is, that researchers face a burden of justification related to any idealizing elements added to trial designs. (shrink)