Title: What is number needed to treat (NNT)? | The BMJ
Headings: What is number needed to treat (NNT)?
What is number needed to treat (NNT)?
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Content: None the less, the larger the treatment effect of supplements (L-arginine and antioxidant vitamins) compared with placebo in reducing the incidence of pre-eclampsia and eclampsia, the smaller the number needed to treat ( d is false). The ideal value for number needed to treat is one, in which case every woman would not experience pre-eclampsia or eclampsia if treated with supplements and all would experience the outcome with placebo. If there was no treatment effect (that is, no difference between supplements and placebo) the absolute risk difference would be zero and the number needed to treat would therefore approach infinity. As with other estimates, it is important the uncertainty in the number needed to treat is assessed by a confidence interval. In the example above, the 95% confidence interval is from 4.0 to 10.0. The 95% confidence limits for number needed to treat are derived in a similar way to the statistic itself. The limits for the 95% confidence interval of the absolute risk difference are obtained; the reciprocal of these are obtained and then reversed, giving the limits of the 95% confidence interval for number needed to treat. The interpretation of the 95% confidence interval is that, with probability of 0.95, the true population parameter of number needed to treat will be contained within the interval—that is, the number of women who need to be treated may be as few as four or as many as 10 in order for one additional woman to benefit compared with if they had been treated with placebo. The challenge is how this degree of uncertainty can be incorporated into clinical decision making.