Calculate the risk ratio and odds ratio from a 2×2 table of exposed and unexposed counts.
| RR | – |
| OR | – |
Use this calculator for a classic 2×2 table: exposed versus unexposed, events versus non-events. Relative risk (risk ratio) compares the two event rates. The odds ratio compares the odds of an event in each row. Cohort sketches and epidemiology homework are typical uses.
Row 1 is exposed (a events, b non-events) and row 2 is unexposed (c events, d non-events). RR = (a / (a + b)) / (c / (c + d)). OR = (a / b) / (c / d). With 20/80 versus 10/90, RR = 2 and OR ≈ 2.25.
A ratio is not a causal stamp. Both rows need a positive total, and non-events (b and d) must be positive for the odds ratio. Zero events in the control row make RR undefined.
Exposed events (a): Events in the exposed group.
Exposed non-events (b): Non-events in the exposed group.
Unexposed events (c): Events in the unexposed (control) group.
Unexposed non-events (d): Non-events in the unexposed group.
RR: Risk ratio, exposed risk divided by unexposed risk.
OR: Odds ratio, (a/b) divided by (c/d).
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