Always ask yourself if fair comparisons of interventions were conducted in circumstances that are relevant.
Some intervention comparisons are designed to find out if an intervention can work under ideal circumstances, for example, in lab conditions or with subjects that are most likely to benefit, and with highly trained practitioners who deliver the intervention exactly as intended.
These comparisons, which are sometimes called ‘explanatory’ or ‘efficacy’ studies, may not reflect what happens under usual circumstances.
REMEMBER: Ask whether intervention comparisons were conducted under ideal circumstances. The results of such studies may overestimate the benefits of the intervention when used under more usual circumstances.