Evidence from clinical trials: can we do better?

Randomized clinical trials provide the most internally valid evidence for medical decision-making. In many areas of neurology, results from clinical trials showing which therapies are and are not effective have had a substantial impact on patient care. Relative to observational methods, the central advantage of clinical trials is control of bias attributable to unmeasured differences between patients. However, trials also have clear limitations, including a historical failure to include a representative cross-section of patients with a given disease, and highly structured treatment regimes that are difficult to replicate in normal practice settings. These limitations tend to reduce the generalizability of results from clinical trials. This article reviews some ways in which the design and application of clinical trials could be improved so that the evidence produced would be more relevant to health-care providers and other decision makers.