efficacy
noun
ef·fi·ca·cy
ˈe-fi-kə-sē 
plural efficacies
: the power to produce a result or effect
increased teacher efficacy in classroom management
The efficacy of this treatment has not yet been proved.
In the upcoming … clinical trial, researchers will further investigate the efficacy and safety of the vaccine.—
Julia Landwehr
Julia LandwehrExamples 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
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
Recent Examples on the Web
Over time, this strengthens self-efficacy and mutual respect, both of which are central to long-term relational stability.
—Mark Travers, Forbes.com, 24 Jan. 2026
Isaacson noted there are decades of research on the efficacy of vaccinations, but things started to change with the COVID-19 pandemic.
—Mike Danahey, Chicago Tribune, 24 Jan. 2026
But in 2015, Holmes was exposed for misleading investors and misrepresenting the efficacy of Theranos’s technology following a series of articles in the Wall Street Journal.
—Jacqueline Munis, Fortune, 23 Jan. 2026
Freezing can also alter the physical properties of medications, leading to inconsistent dosing and reduced efficacy.
—Elissa Robinson, Detroit Free Press, 23 Jan. 2026
See All Example Sentences for efficacy
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Mark Travers, Forbes.com, 24 Jan. 2026
Isaacson noted there are decades of research on the efficacy of vaccinations, but things started to change with the COVID-19 pandemic.
—Mike Danahey, Chicago Tribune, 24 Jan. 2026
But in 2015, Holmes was exposed for misleading investors and misrepresenting the efficacy of Theranos’s technology following a series of articles in the Wall Street Journal.
—Jacqueline Munis, Fortune, 23 Jan. 2026
Freezing can also alter the physical properties of medications, leading to inconsistent dosing and reduced efficacy.
—Elissa Robinson, Detroit Free Press, 23 Jan. 2026
See All Example Sentences for efficacy
Cite this Entry
“Efficacy.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/efficacy. Accessed 28 Jan. 2026.
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