Number needed to treat: Difference between revisions

Revision as of 14:33, 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 p_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 insurers may decline to reimburse drugs with a high NNT.

Worked example

Template:ARR RRR worksheet

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]

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]

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.

External links

Template:WikiDoc Sources

[1] 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.

[pmid11678550-2] 2.0 ^2.1 Richardson A (2001). "Screening and the number needed to treat". J Med Screen. 8 (3): 125–7. PMID 11678550.

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@@ Line 17: / Line 17: @@
 ==Variations==
-===Number needed to screen===
+===Number Needed to Screen===
 In [[Screening (medicine)| screening]], the number needed to screen is the number of patients who must be screened for one patient to benefit.<ref name="pmid11678550">{{cite journal| author=Richardson A| title=Screening and the number needed to treat. | journal=J Med Screen | year= 2001 | volume= 8 | issue= 3 | pages= 125-7 | pmid=11678550 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11678550  }} </ref>
-===Number needed to invite===
+===Number Needed to Invite===
 In [[Screening (medicine)| screening]], the number needed to invite, is the number needed to screen divided by the rate of acceptance of screening.<ref name="pmid11678550">{{cite journal| author=Richardson A| title=Screening and the number needed to treat. | journal=J Med Screen | year= 2001 | volume= 8 | issue= 3 | pages= 125-7 | pmid=11678550 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11678550  }} </ref>