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efficacy

EFF-ih-kuh-see /ˈef.ɪ.kə.si/

nounC1GRESATGMATIELTS

academicmedicalpsychologyformal

The ability to produce a desired or intended result; effectiveness.

Measures capacity to produce intended results under ideal or controlled conditions (e.g., self-efficacy in psychology, vaccine efficacy in medicine).

The story behind the word. Traced to Latin 'efficere' (to bring about, accomplish), combining 'ex-' (out) and 'facere' (to make). Efficacy entered English in the 16th century to measure whether a remedy had the power to make a cure happen.

Word relationships

effectiveness: Effectiveness is general real-world performance, whereas efficacy often implies tested potential under strict conditions.
potency: Potency emphasizes power and strength of effect (especially of drugs).

inefficacy: Lack of power or capacity to produce an intended effect.
futility: Pointlessness or uselessness of action.

Commonly confused with

efficiency: Efficiency is working without wasting time or energy; efficacy is whether the goal is actually achieved.

Word family

efficacious (adjective): Successful in producing a desired result.
efficaciously (adverb): In a manner that produces desired results.

Collocations

self-efficacy
demonstrate efficacy
evaluate efficacy
high efficacy

Example sentences

"Albert Bandura defined self-efficacy as an individual's belief in their capability to execute actions necessary to produce specific performance attainments." Psychological research
"Clinical trials demonstrated the high efficacy of the new antiviral medication." Clinical trials

Memory hook

EFFICACY = EFF-ectiveness in producing a desired CAUSE. Power to produce results.

When not to use

Do not confuse with efficiency; efficiency is doing things with minimal waste, while efficacy is achieving the actual desired outcome.

Fun facts

'Self-efficacy' is one of the most cited concepts in modern psychology, introduced by Albert Bandura in 1977.