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

"There's a pipeline where you've got to prove safety and then prove efficacy, and you've got to do that right," he said.

From BBC

But even if it passes off smoothly and gaffe-free questions may remain about its efficacy.

From BBC

The efficacy of Deen’s waterworks will depend on how much the viewer is willing to buy.

From Salon

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

Related Words

• adequacy 
• competence 
• effectiveness 
• potency 
• virtue