A Primer for Evaluating Clinical Trials

BACKGROUND: Evidence-based medicine demands the use of information from clinical trials to direct medical care. Knowledge of the principles of trial design and conduct is important to assess the validity of results. METHODS: The authors review the key principles behind clinical study design and conduct, and they summarize important biases and confounding issues. RESULTS: Clear hypotheses, a well-described study population, precise measurements, freedom from bias, and consideration of any interactions are attributes of good clinical trials. CONCLUSIONS: The greatest level of evidence in support of a difference in outcome is associated with randomized, controlled clinical trials, particularly when combined with other randomized trials in a systematic fashion (meta-analysis).