Primer: challenges in randomized and observational studies.

Randomized controlled trials (RCTs) are considered superior to observational studies, and both clinicians and researchers believe that conclusions that stem from observational research are flawed. RCTs, however, have important methodological and interpretational limitations, and particular clinical questions can only be addressed by observational research. This Review compares RCTs and observational studies with regard to particular limitations, and explains how the credibility of results from observational studies can be improved by making use of advanced analytical techniques.