efficacy

Sometimes ef·fi·cac·i·ty

[ef-i-kuh-see]

noun

plural

efficacies 

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

/ ˈɛfɪkəsɪ /

noun

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

Other Word Forms

• nonefficacy noun

Word History and Origins

Origin of efficacy¹

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

Example Sentences

With no apparent distance limitations, the missile is meant to get around Western air defense systems, though nuclear scientists doubt the missile’s efficacy.

Read more on The Wall Street Journal

Under the new law, counties can continue to harvest data about the efficacy of their own CalFresh programs.

Read more on Los Angeles Times

The debate over its efficacy and future has raged ever since.

Read more on Los Angeles Times

“There is extremely limited scientific evidence at present that any form of TMS has efficacy and safety in improving the core symptoms of language, social skills, or behavioral disturbances associated with ASD,” the editorial states.

Read more on Los Angeles Times

The technique is used around the world, but experts doubt its efficacy as a long-term air pollution control measure.

Read more on BBC

Related Words

• adequacy 
• competence 
• effectiveness 
• potency 
• virtue