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efficacy

noun [U]
 
 
/ˈef.ɪ.kə.si/ formal

Definition

an ability, especially of a medicine or a method of achieving something, to produce the intended result: They recently ran a series of tests to measure the efficacy of the drug. → Synonym effectivenessEfficient and effective
(Definition of efficacy noun from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

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