effectiveness

American  

[ih-fek-tiv-nis, ee-fek‐] / ɪˈfɛk tɪv nɪs, iˈfɛk‐ /

Rarely effectivity

noun

1. the quality of producing an intended or desired result.

   For maximum effectiveness of your weight loss plan, you need to combine exercise with a healthy diet.

2. the quality of producing a deep or vivid impression.

   We were struck by the evident appeal and effectiveness of these short, dramatic, upbeat video stories.

3. a measure of the success of a vaccine or other pharmaceutical when used in the real world, as opposed to the controlled environment of a clinical trial.

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Other Word Forms

• subeffectiveness noun
• supereffectiveness noun
• uneffectiveness noun

Etymology

Origin of effectiveness

First recorded in 1600–10; effective ( def. ) + -ness ( def. )

Example Sentences

There’s a chunk of code for a memory system to keep the context of conversations going without overloading the AI with too much information—a problem known to amplify hallucinations and reduce the effectiveness of guardrails.

From The Wall Street Journal • Apr. 17, 2026

In March 2025, Kennedy issued a statement that noted vaccines’ effectiveness in preventing measles’ spread, but stopped short of outright recommending that parents vaccinate their children.

From Los Angeles Times • Apr. 16, 2026

Intense competition is pushing manufacturers to improve effectiveness while slashing costs, sometimes to less than $1,000 per unit, making them "affordable", Myronenko said.

From Barron's • Apr. 9, 2026

By analysing millions of their genetic variants, the researchers found a pattern suggesting a link between some variants and the effectiveness of the drugs.

From BBC • Apr. 8, 2026

And I judge the effectiveness of that job not so much by obedience to rule, for rules can be enforced, but by the humor of the general prison population.

From "Newjack: Guarding Sing Sing" by Ted Conover

Related Words

• capability
• efficacy
• efficiency
• potency
• power
• success