What this calculator does
Fisher's exact test works out runs a two-tailed Fisher exact test on a 2×2 contingency table of counts. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaP(table) = (a+b)!(c+d)!(a+c)!(b+d)! / (a!b!c!d!n!). Two-tailed p-value sums P over all tables (same margins) with P ≤ P(observed)
The inputs explained
| Field | What to enter |
|---|---|
| Group 1, outcome A | A number. Starts at 8. |
| Group 1, outcome B | A number. Starts at 2. |
| Group 2, outcome A | A number. Starts at 1. |
| Group 2, outcome B | A number. Starts at 9. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with group 1, outcome a
Every other input is held at the calculator’s starting values while group 1, outcome a varies. Select any row to load that scenario into the calculator.