# Absolute vs relative risk

Absolute risk (AR) is the probability that you experience an event, like a heart attack, a cancer diagnosis, or death, within a defined time period. Relative risk (RR) expresses that probability as a ratio, compared with a reference group. And the relative risk reduction (RRR) is the proportional fall in the event rate between treated and untreated groups. Here is the key point. RRR is independent of baseline risk. So a drug that cuts cardiovascular events from 2% to 1%, and one that cuts them from 40% to 20%, both give a 50% RRR. Yet their absolute risk reductions (ARR) are very different: 1 versus 20 percentage points. That means numbers needed to treat (NNT, the inverse of ARR) of 100 versus 5. In longevity and preventive medicine, baseline event rates are low in healthy middle-aged adults. So interventions framed as cutting risk by 30 to 40% often 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 the underlying absolute risks alongside the ratio measures (Schwartz et al. 2006). That inflates the perceived benefit. So a sound appraisal of any longevity intervention needs ARR and NNT alongside RRR. When baseline risk is low, even a large RRR may reflect a small absolute gain.

## Sources

- Schwartz LM, Woloshin S, Dvorin EL, et al.. (2006). Ratio measures in leading medical journals: structured review of accessibility of underlying absolute risks. BMJ. https://doi.org/10.1136/bmj.38985.564317.7C
- Ranganathan P, Pramesh CS, Aggarwal R. (2016). Common pitfalls in statistical analysis: Absolute risk reduction, relative risk reduction, and number needed to treat. Perspectives in Clinical Research. https://doi.org/10.4103/2229-3485.173773
- Brown RB. (2022). Relative risk reduction: Misinformative measure in clinical trials and COVID-19 vaccine efficacy. Dialogues in Health. https://doi.org/10.1016/j.dialog.2022.100074

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