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Odds ratio and relative risk calculator
Enter a 2×2 table. You get the odds ratio and risk ratio with 95% confidence intervals, absolute risk reduction, number needed to treat, a chi-square test, and a sentence you can paste into your results.
Confounding, selection and measurement bias all sit between this number and a claim about cause. Adjusting for them requires a model, not a 2×2 table — and it is the first thing a reviewer will ask about.
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This calculator was checked by Sidra Khan, Lead Biostatistician
In short
How do you calculate an odds ratio?
An odds ratio is the odds of an outcome in the exposed group divided by the odds in the unexposed group, calculated from a 2×2 table as (a×d)/(b×c). Its 95% confidence interval is found on the log scale. If the interval excludes 1, the association is statistically significant at the 5% level.
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