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Compound Evidence InstituteEvidence synthesis · established 2023Graded assessments of compounds, trials, methods and supply
Document set current to 30 July 2026
Defined term · Outcomes and endpoints

Number needed to harm

The reciprocal of the absolute risk increase for a harm. Reported alongside the number needed to treat wherever both are estimable.

Document identifier
CEI-GT-101
Series
Defined term
Version
1.0
Published
30 Jul 2026
Last reviewed
30 Jul 2026
Certainty
Not rated

§1Number needed to harm

§1.1Also known as

NNH

§1.2Category

Outcomes and endpoints — Terms describing what a study measures and what the measurement supports.

§1.3Related terms

  • Number needed to treat — The reciprocal of the absolute risk difference: the number of people who must be treated for the stated duration for one additional person to benefit. Rises sharply as…
Compound Evidence Institute · CEI-GT-101 · https://compoundevidence.com/glossary/number-needed-to-harm/ · retrieved 30 July 2026
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