Calculation of the number needed to treat |
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From "Using Numeric Results from Systematic Reviews in Clinical Practice." Annals of Internal Medicine , 1 May 1997. 126:712-720.
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Figure 2. Calculation of the number needed to treat (NNT) from odds ratios. Tables for estimating the NNT when the odds ratio (OR) and control event rate (CER) are known, published for preventive interventions in reference 28. The formula for determining the NNT for preventive interventions is {1 - [ CER X (1 - OR )]}/[1 - CER ) X CER X (1- OR )]. For treatment, the formula is [ CER ( OR - 1) + 1]/[ CER ( OR -1) X (1 - CER )].
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