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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- 1 Medicine Department, Southland Hospital, Invercargill, New Zealand.
- 2 Drug Usage and Assessment Group, Royal Perth Hospital, Perth, WA.
- 3 Finance and Business Services, Royal Perth Hospital, Perth, WA.
Correspondence: alasdair.millar@sdhb.govt.nz
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