Confidence intervals for the number needed to treat

BMJ 1998;317:1309-1312 ( 7 November )

Education and debate

Confidence intervals for the number needed to treat

Douglas G Altman, professor of statistics in medicine.

Imperial Cancer Research Fund Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Oxford OX3 7LF

d.altman@icrf.icnet.uk

The first 150 words of the full text of this article appear below.

The number needed to treat (NNT) is a useful way of reporting the results of randomised controlled trials.¹ In a trialcomparing a new treatment with a standard one, the number neededto treat is the estimated number of patients who need to be treatedwith the new treatment rather than the standard treatment forone additional patient to benefit. It can be obtained for anytrial that has reported a binaryoutcome.

Table Removed (Available Only in the Full Text)

Trials with binary end points yield a proportion of patients in each group with the outcome of interest. When the outcomeevent is an adverse one, the difference between the proportionswith the outcome in the new treatment (p_N) and standard treatment(p_S) groups is called the absolute risk reduction (ARR=p_N $-$ p_S).The number needed to treat is simply the reciprocal of the absoluterisk difference, or 1/ARR (or 100/ARR if percentages are used. . . [Full text of this article]

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Rapid Responses:

Read all Rapid Responses

Limits of confidence in pooled NNT results: Christopher Cates
bmj.com, 11 Nov 1998 [Full text]
Confidence intervals for the number needed to treat: Robert G Newcombe
bmj.com, 5 Jan 1999 [Full text]