Evaluation of randomized controlled trials.

Although randomized controlled trials (RCTs) play a key role in modern medicine, considerable variability exists in their quality and in the reliability (reproducibility) of their results. The present article discusses features that characterize high-quality trials, such as intent-to-treat (ITT) analysis, the avoidance of patient exclusions, and a procedure for evaluating the reliability of study results. A single serious problem can sometimes invalidate a study. However, most often one must weigh the impact of various strengths and weaknesses of aspects of study design, conduct, and analysis. A companion article1 on the design of RCTs appeared in a previous issue of this journal.