Odds ratio
One group's odds of an outcome divided by another group's odds. Close to the risk ratio when the outcome is rare, but much larger than it when the outcome is common.
In plain English
Odds are the chance something happens divided by the chance it doesn't. Odds ratios come out of case-control studies and logistic regression, so they're everywhere in health research. The trap is reading them as 'times more likely': with a common outcome, an odds ratio of 2.67 can mean only a third more likely.
Uncle Gary explains
With a tutor 80% pass (odds 4.0), without 60% (odds 1.5): the odds ratio is 2.67 but the risk ratio is only 1.33.
Why it matters for your money
A headline that says a habit 'doubles your odds' of a common outcome is usually describing a much smaller change in actual chances. Convert back to probabilities before acting on it.
Where we tested it
Related terms
All glossary terms. Educational content, not financial advice.