To the Editor: The clinical justification for a medical intervention depends on absolute prevalence (p) of a disease or condition in a population and the relative risk reduction (R) that would result from the intervention. These variables determine the “number needed to treat” (NNT) to prevent one occurrence of a disease, according to the formula NNT = [100 ÷ (P × R)], where P and R are expressed as percentages.
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