Fisher's Exact Test Calculator
Perform Fisher's exact test on a 2x2 contingency table to test whether there is a significant association between two categorical variables. Unlike the chi-square test, Fisher's exact test gives exact p-values and works with small sample sizes.
Fisher's exact test computes the exact probability of observing the data (or more extreme) under the null hypothesis of no association. It enumerates all possible 2x2 tables with the same marginal totals and sums the probabilities of tables as extreme as or more extreme than the observed one.
When to use Fisher's exact test: Use it when any expected cell count in your 2x2 table is less than 5, or when you want an exact (rather than approximate) p-value. For larger samples, it gives the same conclusions as the chi-square test but is computationally more demanding.
Odds ratio and relative risk: The odds ratio (OR = ad/bc) measures the strength of association on the odds scale. An OR of 1 means no association. The relative risk (RR) compares the probability of the outcome between groups and is often more intuitive in medical studies.