Fisher exact test calculator
Enter the four counts of a 2 by 2 table. The calculator keeps margins fixed and sums probabilities of the relevant tables.
Tables with the same margins
| a | b | c | d | Probability |
|---|---|---|---|---|
| Fill in the fields above — the result is computed on this page. | ||||
How to use this page
- Enter four non-negative counts.
- Choose the alternative direction.
- Read the exact p-value and odds ratio.
What this page does not do: With zero cells the raw odds ratio may be infinite or undefined. This calculator does not compute an odds-ratio confidence interval.
Further reading
Fisher's exact test examines association between two binary variables in a 2 by 2 table. Each table probability follows a hypergeometric distribution conditional on row and column totals.
The two-sided p-value sums probabilities of tables no more probable than the observed table. An odds ratio above 1 indicates positive association for the chosen cell arrangement.
Frequently asked questions
When should I use Fisher rather than chi-square?
Especially when expected counts are small in a 2 by 2 table.
Is the result exact?
Yes for the fixed margins and selected tail definition; it does not use an asymptotic p approximation.
See also
Beta distribution calculator
Calculate beta density, CDF, upper tail and quantile together with its mean and variance.
Chi-square test calculator
Calculate chi-square goodness of fit, independence, or a chi-square critical value.
Continuous uniform distribution calculator
Calculate density, CDF, upper tail, quantile, mean and variance for U(a,b).