Absolute vs relative risk

Absolute risk (AR) is the probability that an individual experiences an event — such as a heart attack, cancer diagnosis, or death — within a defined time period. Relative risk (RR) expresses that probability as a ratio compared with a reference group; relative risk reduction (RRR) is the proportional fall in event rate between treated and untreated groups. Because RRR is independent of baseline risk, a drug reducing cardiovascular events from 2% to 1% and one reducing them from 40% to 20% both yield a 50% RRR, yet their absolute risk reductions (ARR) are 1 and 20 percentage points respectively — giving numbers needed to treat (NNT, the inverse of ARR) of 100 versus 5. In longevity and preventive medicine, where baseline event rates are low in healthy middle-aged adults, interventions framed as cutting risk by 30–40% frequently reduce absolute risk by fewer than 2 percentage points over five years. A structured review of 222 articles in six leading journals — including BMJ, NEJM, and JAMA — found that 68% omitted underlying absolute risks alongside ratio measures (Schwartz et al. 2006), inflating perceived treatment benefit. Sound appraisal of any longevity intervention requires ARR and NNT alongside RRR; when baseline risk is low, even a large RRR may reflect a small absolute gain.