Number needed to treat

The number needed to treat (NNT) is an epidemiologicalmeasure that indicates how many patients would require treatment with a form of medicationto reduce the expected number of cases of a defined endpoint by one. It is defined as the inverse of the absolute risk reduction.

For example, consider a hypothetical drug which reduces the risk of colon cancerby 50%. Even without the drug, colon cancer is pretty rare, let's say 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, you 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 probabilitiesp_A and p_B of this endpoint under treatments A and B, respectively, are known, then the NNT is computed as 1/(p_B-p_A).

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 insurersmay decline to reimburse drugs with a high NNT.

See also

• Number needed to harm- the converse for side-effects

External link

• Bandolier article on NNT

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It uses material from the http://en.wikipedia.org/wiki/Number+needed+to+treat Wikipedia article Number needed to treat.