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Related Experiment Video

Updated: Jul 9, 2026

Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling
20:36

Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling

Published on: July 4, 2007

The number needed to harm: is it too optimistic?

D Massel1

  • 1Department of Medicine, University of Western Ontario, London, Canada. dmassel@lhsc.on.ca

The Canadian Journal of Cardiology
|February 5, 2004
PubMed
Summary
This summary is machine-generated.

The number needed to treat (NNT) and number needed to harm (NNH) help interpret clinical trial outcomes. NNH quantifies patient harm from treatments, but may underestimate true risks.

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Area of Science:

  • Clinical research methodology
  • Medical statistics
  • Pharmacovigilance

Background:

  • Clinical trials assess therapeutic benefits and risks.
  • Interpreting treatment outcomes requires understanding both positive and negative effects.
  • Existing metrics like NNT focus on benefits, necessitating complementary harm assessment.

Purpose of the Study:

  • To introduce and define the number needed to harm (NNH) as a measure for adverse outcomes in clinical trials.
  • To highlight the relationship between NNH and the absolute risk increase.
  • To discuss the potential limitations of NNH in reflecting true therapeutic risks.

Main Methods:

  • Conceptual definition of NNH based on absolute risk increase.
  • Comparison of NNH with the number needed to treat (NNT).
  • Discussion of the interpretation of NNH in the context of experimental vs. control treatments.

Main Results:

  • NNH is defined as the reciprocal of the absolute risk increase.
  • NNH represents the number of patients exposed to an experimental treatment for one additional harm event.
  • NNH may present an optimistic view of treatment-related risks.

Conclusions:

  • NNH is a valuable metric for quantifying patient harm in clinical studies.
  • Understanding NNH is crucial for a balanced interpretation of treatment efficacy and safety.
  • Further consideration is needed to address the potential underestimation of risks by NNH.