12.5.4.3  Computing absolute risk reduction or NNT from an odds ratio (OR)

Review authors may wish to compute an absolute risk reduction or NNT from the results of a meta-analysis of odds ratios. In order to do this, an assumed control risk (ACR) is required. It will usually be appropriate to do this for a range of different ACRs. The computation proceeds as follows:

 

As an example, suppose the odds ratio is OR = 0.73, and a control risk of ACR = 0.3 is assumed. Then the effect on risk is 62 fewer per 1000:

 

The NNT is 17:

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