Until recently clinical decision‐making relied on intuition, unsystematic experiences and ‘pathophysiological rationale. Developments in the understanding of the nature of clinical trials, systematic reviews and techniques to evaluate diagnostic technology over the past 30 years made the evidence‐based clinical practice possible. During this period of evolution it became apparent that not all evidence is equal. Studies that use weak designs tend to estimate a greater treatment effect, whereas strong designs yield a more conservative treatment effect. A good number of orthodontic problems lend themselves to investigations of controlled clinical trials. Reports of early treatment effectiveness of malocclusions contained in this issue demonstrate the point.