efficacy
n. uncountablen. the ability of something to produce the result you want. You use this word when you are talking about how well a treatment or a plan actually works.
n. the power or capacity to produce a desired or intended result. Often used in medical, scientific, or policy contexts to describe the effectiveness of a specific intervention.
The doctors are testing the efficacy of the new medicine.
Recent clinical trials have demonstrated the high efficacy of the vaccine in preventing severe illness among elderly patients.
While the theoretical model was sound, the actual efficacy of the policy depended heavily on the cooperation of local administrators and the availability of consistent funding.
From Old French efficace, from Late Latin efficācia (“efficacy”), from efficāx (“efficacious”); see efficacious.
Uncountable in its abstract sense; often paired with 'of' to specify the subject being measured.
the efficiency of the drugthe efficacy of the drugLearners often use 'efficiency' (doing things without waste) when they mean 'efficacy' (the power to produce a result).