Odds ratio, relative risk, and risk difference
Effect sizes with 95% confidence intervals from a 2 × 2 table.
Inputs
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When to use
- Appraising a trial or cohort study.
Pearls and pitfalls
- OR approximates RR only when the outcome is rare (under about 10%).
- A zero cell needs a continuity correction (0.5 is added here).
Why use
All three effect sizes, with intervals, from one table.
OR = (a × d) ÷ (b × c); RR = (a ÷ (a + b)) ÷ (c ÷ (c + d)); 95% CI = exp(ln estimate ± 1.96 × SE)