A preventive measure that brings large benefit to a population offers little to each individual who takes part in it.
Rose set it out in 1981. Most cases of a common disease arise in the large group at moderate risk rather than the small group at high risk, so shifting the whole distribution prevents more cases than treating the extreme. The individual arithmetic is discouraging: of the many who take the drug, wear the helmet or accept the restriction, almost all would have been fine and one or two are saved. Population measures therefore depend on a compliance that can never be justified case by case.
In practice
- A road safety rule inconveniences a million drivers a day and prevents a handful of deaths a year, which its critics and its authors are both right about.
- A patient asks what a statin will do for him, and the honest answer is that it will probably do nothing for him and something for people like him.
- Standing
- A consequence of how risk is distributed rather than a disputed finding, and the standing reason that public health measures are unpopular with the individuals they protect. Compare the base rate fallacy.
- Subject
- Risk & Reliability
- Essay
- How accidents actually happen