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

An activist group he ran for eight years, Children's Health Defense, repeatedly questioned the safety and efficacy of vaccination.

From BBC

She felt that they took no real accountability for the pitfalls of their product, and was let down by their decision to continue selling it for two months despite doubts over its efficacy.

From BBC

Battered by this constant deluge of information, audiences have lost their ability to appreciate not only the art of satire, but its efficacy.

From Salon

The states said the focus of their health alliance will be on ensuring the public has access to credible information about the safety and efficacy of vaccines.

From Los Angeles Times

While Kennedy has endorsed the vaccine as the best way to prevent the spread of measles, he has also made false claims about the safety and efficacy of the shot.

From BBC

Related Words

• adequacy 
• competence 
• effectiveness 
• potency 
• virtue