Numbers needed to treat derived from meta-analysis: a word of caution.

In the editorial by Drs Marx and Bucher in the March/April 2003 issue of Evidence-Based Medicine, an example illustrating the application of estimates of RRRs to individual risk is misleading. In their example, Marx and Bucher state that the NNTwould increase in patients with a baseline risk 11 times that of the low risk group, which is counterintuitive. If a high risk patient is judged to have a risk greater than that of a low risk patient, the NNT would be expected to decrease, not increase. I believe they meant to say that the NNT divided by the factor f will yield the adjusted risk of outcome in an individual patient.