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==Overview== | ==Overview== | ||
Revision as of 14:41, 25 September 2014
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
The number needed to treat (NNT) is an epidemiological measure that indicates how many patients would require treatment with a form of medication to reduce the expected number of cases of a defined endpoint by one. It is defined as the inverse of the absolute risk reduction. It was described in 1988.[1]
For example, consider a hypothetical drug which reduces the risk of colon cancer by 50%. Even without the drug, colon cancer is fairly rare, maybe 1 in 3,000 in every 5 year period. The NNT for a 5-year treatment with the drug is therefore 6,000: by treating 6,000 people with the drug, one can expect to reduce the number of colon cancer cases from 2 to 1.
In general, NNT is always computed with respect to two treatments A and B, with A typically a drug and B a placebo (in our example above, A is a 5-year treatment with the hypothetical drug, and B is no treatment). A defined endpoint has to be specified (in our example: the appearance of colon cancer in the 5 year period). If the probabilities pA and pB of this endpoint under treatments A and B, respectively, are known, then the NNT is computed as 1/(pB-pA).
The NNT is an important measure in pharmacoeconomics. If a clinical endpoint is devastating enough (e.g. death, heart attack), drugs with a high NNT may still be indicated in particular situations. If the endpoint is minor, health insurers may decline to reimburse drugs with a high NNT.
Worked example
Variations
Number Needed to Screen
In screening, the number needed to screen is the number of patients who must be screened for one patient to benefit.[2][3]
Number Needed to Invite
In screening, the number needed to invite, is the number needed to screen divided by the rate of acceptance of screening.[2]
See also
- Number needed to harm - the converse for side-effects
Reference
- ↑ Laupacis A, Sackett DL, Roberts RS. An assessment of clinically useful measures of the consequences of treatment. N Engl J Med 1988;318:1728-33. PMID 3374545.
- ↑ 2.0 2.1 Richardson A (2001). "Screening and the number needed to treat". J Med Screen. 8 (3): 125–7. PMID 11678550.
- ↑ Rembold CM (1998). "Number needed to screen: development of a statistic for disease screening". BMJ. 317 (7154): 307–12. PMC 28622. PMID 9685274.