efficacy

noun
ef·​fi·​ca·​cy | \ ˈe-fi-kə-sē How to pronounce efficacy (audio) \
plural efficacies

Definition of efficacy

: the power to produce an effect

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Examples of efficacy in a Sentence

In the planner's view, Rumsfeld had two goals: to demonstrate the efficacy of precision bombing and to "do the war on the cheap." — Seymour M. Hersh, New Yorker, 7 Apr. 2003 Vaccines exist, but their efficacy against aerosolized plague is unknown. — Sharon Begley et al., Newsweek, 8 Oct. 2001 efficacy does not have to be demonstrated before homeopathic products are marketed. — Alison Abbott et al., Nature, 26 Sept. 1996 questioned the efficacy of the alarms in actually preventing auto theft
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Recent Examples on the Web

Moreover, early data from the Southern Hemisphere—which can offer a glimpse of what’s to come in the US—suggested that last year’s flu vaccine had an abysmal 10 percent efficacy rate. Beth Mole, Ars Technica, "Last year’s flu was brutal—killing 80,000—but vaccine did better than expected," 27 Sep. 2018 The art lies not only in the fresh efficacy of idea and utterance, but in the story’s armature, its determining designs. William Giraldi, The Seattle Times, "Glen David Gold’s new memoir is ‘a soiree of heart-wreck wised up by humor’," 9 July 2018 Reviews are still stalled because none of the manufacturers has submitted additional safety and efficacy data, said FDA spokeswoman Sandy Walsh. Jack Kaskey, chicagotribune.com, "Your outdated sunscreen exposes you to needless cancer risk," 30 May 2018 Opinions on the efficacy of charcoal toothpaste are split. Laura Daily, The Seattle Times, "How charcoal escaped the grill and ended up in your bathroom," 12 Apr. 2019 True Genius reporter James Vincent even made the actual butterfly from the image a custom emoji for the Vox Media Slack, which only added to its efficacy. Verge Staff, The Verge, "The best memes of 2018, according to The Verge staff," 27 Dec. 2018 Levonorgestrel decreases in efficacy over time and doesn’t work as effectively after a sharp uptick of luteinizing hormone (LH) tells one of your ovaries to release an egg for fertilization. Natasha Lavender, SELF, "7 Myths About Emergency Contraception You Should Stop Believing," 8 Apr. 2019 There are no warnings about efficacy and weight on the package of the emergency contraception Plan B even though evidence suggests that the morning-after pill might be less effective for heavier women. Macaela Mackenzie, Glamour, "What Shrill Gets Right—and Wrong—About the Morning-After Pill Weight Limit," 15 Mar. 2019 But generally speaking, the medical community’s concerns about the vaginal lightening trend have less to do with efficacy and more to do with safety. E.j. Dickson, Vox, "The dangerous rise of vaginal lightening," 6 Dec. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'efficacy.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of efficacy

13th century, in the meaning defined above

History and Etymology for efficacy

borrowed from Latin efficācia, from efficāc-, efficāx "capable of fulfilling a function, efficacious" + -ia -y entry 2

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Statistics for efficacy

Last Updated

5 Jun 2019

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Time Traveler for efficacy

The first known use of efficacy was in the 13th century

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More Definitions for efficacy

efficacy

noun

English Language Learners Definition of efficacy

formal : the power to produce a desired result or effect

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Comments on efficacy

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