Efficacy Meaning
/ˈɛf.ɪ.kə.si/Definition, CEFR level C1, pronunciation, examples, and quiz.
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Definition
nounThe ability to produce a desired effect under ideal testing conditions.
nounA degree of ability to produce a desired effect; effectiveness.
Sentence Examples
Don't confuse "efficacy" with "efficiency".
This practice is of dubious efficacy.
CEFR Practice Quiz
Scientists questioned the ____ of the vaccine after many patients still got sick.
CEFR Practice Quiz (Alternate)
The researchers studied the ____ of the new drug to determine its effectiveness in treating the disease.
Word Origin & History
From Old French efficace, from Late Latin efficācia (“efficacy”), from efficāx (“efficacious”); see efficacious.
Literary Quotations & Historical Citations
"[…]and this hath even made me ſuſpect the efficacy of reliques, to examine the bones, queſtion the habits and appurtenances of Saints, and even of Chriſt himſelf."
— 1642, Sir Thomas Browne, “Religio Medici [The Religion of a Doctor]”, in The Works Of the Learned Sr Thomas Brown, Kt., London: Tho. Basset et al., published 1686, page 15:
"No method of verification known to science is applicable to the efficacy of prayer. […] If, then, the efficacy of prayer eludes the test of science, and if even uncertainty may rest upon the connection between an event asked in prayer, and the prayer that sought it, is there any evidence by which the efficacy of prayer may be tested and known?"
— 1875, Rev. Professor Wallace, “Prayer in Relation to Natural Law”, in Science and Revelation, Belfast: William Mullan, →ISBN, page 43:
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CEFR Practice Quiz
Scientists questioned the ____ of the vaccine after many patients still got sick.
CEFR Practice Quiz (Alternate)
The researchers studied the ____ of the new drug to determine its effectiveness in treating the disease.