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Numbers needed to treat derived from meta-analysis: a word of caution.
  1. Daniel Peterson, MD
  1. St. Luke’s-Roosevelt Hospital Center
 New York, New York, USA

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    In the editorial by Drs Marx and Bucher in the March/April 2003 issue of Evidence-Based Medicine,1 an example illustrating the application of estimates of RRRs to individual risk is misleading. In their example, Marx and Bucher state that the NNT would 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.