The ability to produce a desired effect under ideal testing conditions.
2005, Flay et al. Standards of Evidence: Criteria for Efficacy, Effectiveness and Dissemination DOI: 10.1007/s11121-005-5553-y
Efficacy refers to the beneficial effects of a program or policy under optimal conditions of delivery, whereas effectiveness refers to effects of a program or policy under more real-world conditions.
A degree of ability to produce a desired effect; effectiveness.
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