efficacy – the ability to produce the results that were intended

(Pronounced eh-fik-uh-see)

To remember the definition of the word efficacy, use the following mnemonic:

Her effort to flick with accuracy (efficacy) required great concentration, but she always had the ability to produce the intended results. 

Examples of efficacy in a sentence

The low efficacy of the drug caused it to fail the trials. 

She was evaluating the efficacy of their new sales tactics. 

The efficacy of his teaching methods was brought into question.