Relative Risk
Etymology
“Relative” is from Latin “referre” (to carry back). “Risk” entered English via Italian “rischio,” whose deeper origin is disputed — proposed sources include a verb for “to dare” and older nautical terms for hazard — so etymologists leave it unresolved.
noun phrase · /REL-uh-tiv RISK/
How much a risk changes in proportion — such as “doubles” — as opposed to by how much in absolute terms.
What it names
It exposes the favorite trick of scary headlines: a big percentage change on a tiny underlying chance.
Example
“Bacon raises bowel-cancer risk by 18 percent” is relative risk; in absolute terms it may nudge a lifetime chance from about 5 to 6 percent.
Related idea
Relative risk without the base rate is nearly meaningless — a 100 percent increase on a one-in-a-million risk is still one-in-500,000; always ask for the absolute risk, and beware base-rate neglect.