Number needed to treat (NNT)

The number needed to treat (NNT) is the average number of patients who must receive an intervention for one additional patient to benefit over control. Introduced by Laupacis, Sackett, and Roberts in the New England Journal of Medicine (1988), NNT is the reciprocal of the absolute risk reduction (ARR): NNT = 1 ÷ ARR, where ARR equals the control-arm event rate minus the treatment-arm event rate. Because NNT anchors benefit to a concrete patient count, it makes absolute effect size transparent: an NNT of 50 means 50 people must be treated for one to avoid the target outcome. In aging and longevity medicine — where interventions target prevention of cardiovascular disease, cancer, or functional decline — NNT values are often far higher than intuition suggests. A re-analysis of the JUPITER trial (Ridker et al., 2009) found an NNT of 95 for the primary composite endpoint among the lowest-risk participants receiving 5-year rosuvastatin; statins in true primary prevention for healthy adults carry NNTs of 60-270 depending on endpoint and risk stratum. NNT depends critically on baseline risk, observation period, and comparator; a figure cited without this context can mislead, and confidence intervals derived from the ARR are essential for proper interpretation.