Fisher Exact Test Calculator
Calculate the exact p-value for a 2x2 contingency table using Fisher's exact test. Useful for small sample sizes to determine if there are nonrandom associations between two categorical variables.
Published by:
isCalculator Editorial Team
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How to use this tool?
This calculator performs a Fisher Exact Test on a 2x2 contingency table. Use it to determine if there is a non-random association between two categorical variables when sample sizes are small.
Step-by-Step Instructions
- Enter cell counts — Input non-negative integers into the four fields labeled a, b, c, and d representing your 2x2 table:
- a = Group 1, Outcome 1
- b = Group 1, Outcome 2
- c = Group 2, Outcome 1
- d = Group 2, Outcome 2
- Click "Calculate P-Value" — The button processes your data instantly.
- Read the result — The output shows:
- The two-sided p-value (rounded to 6 decimal places).
- A summary of the table, row/column totals, and the calculation steps.
Important Notes
- All four cells must contain non-negative integers (0 or greater).
- The total count must be greater than zero.
- This test is ideal for small sample sizes (e.g., when any expected cell count is less than 5).
- A low p-value (typically < 0.05) suggests a statistically significant association between the groups and outcomes.
Previous Results
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Frequently Asked Questions
Fisher's exact test is a statistical significance test used in the analysis of contingency tables. It is used to determine if there are nonrandom associations between two categorical variables, especially when sample sizes are small.
Fisher's exact test is recommended when any expected cell count is less than 5, as it provides an exact p-value rather than an approximation. It is also suitable for small sample sizes overall.
The p-value is calculated by summing the probabilities of all tables with the same row and column totals that have a probability less than or equal to the observed table. The probability of each table follows a hypergeometric distribution.
