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number needed to harm (NNH)

1/absolute risk increase. For example, if risk with treatment is 20% vs 5% for placebo, the absolute risk increase is 0.20-0.05 = 0.15. Thus, the number need to harm is 1/0.15 = 6.667 ~ 7 The number of patients needed to treat for a single patient to be harmed.

Related

relative risk reduction (RRR)

General

statistics (biostatistics)

References

  1. Medical Knowledge Self Assessment Program (MKSAP) 16, 17. American College of Physicians, Philadelphia 2012, 2015
  2. The NNT: Quick summaries of evidence-based medicine. http://www.thennt.com/