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Efficacy versus Effectiveness

The terms efficacy and effectiveness refer to different concepts and are not interchangeable. In general, efficacy refers to whether an intervention works under ideal conditions for a specific outcome. Effectiveness refers to a broader view of the usefulness of an intervention in the routine care of patients in the day-to-day practice of medicine. Efficacy is measured using controlled clinical trials, using specific outcome measures, such as prespecified changes in rating scales or laboratory parameters. Examples of efficacy studies are medication registration trials testing drug versus placebo. Effectiveness is measured by a variety of methods, including synthesis of efficacy and tolerability clinical trial data, clinical trials that incorporate broad outcomes such as quality of life, longitudinal prospective naturalistic studies, and retrospective studies using large-scale clinical, pharmacy, ...

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