The odds ratio divides the odds of exposure among cases by the odds among controls. It is the measure produced by case-control studies, where incidence cannot be calculated because subjects are selected by disease status.
It approximates relative risk when the disease is rare.
Alternative Names:
OR, Odds Ratio Estimate
Why it Matters?
The rare disease assumption is the interpretive limitation, since the odds ratio overstates relative risk as disease prevalence rises. For rare cancers the approximation holds well, which is why case-control studies are standard in cancer epidemiology. Treating an odds ratio as equivalent to relative risk for a common condition overstates the association, and that substitution is worth checking in expert reports.
Frequently Confused with
Related terms
Frequently asked questions
When does an odds ratio approximate relative risk?
What is the interpretive error to watch for?
