The applicability and generalizability of findings from clinical trials for health-policy decisions.

Randomized controlled trials provide unbiased estimates of treatment effect through reducing the attribution of observed differences in outcome to the play of chance or the treatment of interest. Issues in the design of randomized trials may lead to a dilution or magnification of treatment effect when compared with clinical practice. The intention-to-treat principle will lead to dilution in the treatment effect, while the selective recruitment of adherent and motivated subjects may lead to enhanced treatment effect estimates. Observational data, on the other hand, may reflect clinical practice but cannot provide unbiased estimates of treatment effect. Health policy may be informed by the combination of randomized and observational data in decision-analytic models.