efficacy

American  

[ef-i-kuh-see] / ˈɛf ɪ kə si /

Sometimes efficacity

noun

efficacies plural

1. the capacity for producing a desired result or effect.

   Short, frequent periods of practice were shown to have greater efficacy than longer and less frequent ones.

2. a measure of the success of a vaccine or other pharmaceutical when used in the controlled environment of a clinical trial, as opposed to in the real world.

---

efficacy British  

/ ˈɛfɪkəsɪ /

noun

1. the quality of being successful in producing an intended result; effectiveness

---

Other Word Forms

Derived Forms

• nonefficacy
  noun

Inflected Forms

noun

• efficacies
  plural

Etymology

Origin of efficacy

First recorded in 1520–30; from Latin efficācia, from efficāc- (stem of efficāx ) “effective, effectual” + -ia, noun suffix; see efficacious ( def. ), -y ³ ( def. )

Explanation

The degree to which a method or medicine brings about a specific result is its efficacy. You might not like to eat it, but you can't question the efficacy of broccoli as a health benefit. Efficacy is a more formal way to say effectiveness, both of which stem from the Latin verb efficere "to work out, accomplish." The effectiveness, or efficacy, of something is how well it works or brings the results you hoped for. A scientist does research to determine the efficacy of a vaccine or medicine under development. If it is efficacious, it will cure or prevent a disease.

Related Words

• adequacy
• competence
• effectiveness
• potency
• virtue