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