Fisher's Exact Test

What is the Fisher’s Exact Test?

Fisher’s exact test, also called Fisher’s exact test of independence, is a test of statistical significance used in the analysis of contingency tables, also known as a cross tabulation. It is used when you have two nominal variables, which are a type of categorical variable that assumes no order or rank for the categories. The Fisher’s exact test is used to investigate if proportions for one nominal variable are different among values of the other nominal variable. It is used in practice for experiments with a small number of participants. 

Why is this Useful?

With the Fisher’s exact test we can compare proportions of two nominal variable outcomes. This test is used in practice for the analysis of small sample sizes, but it is actually valid for all sample sizes. Fisher’s exact test is used instead of chi-squared tests when more than 20% of cells have expected frequencies less than 5, and if any one cell is expected to be less than 1 in a cross tabulation. Chi-squared tests are based on approximation methods and Fisher’s exact test are based on exact methods, with small cell sizes the Fisher’s exact test is more appropriate. 

Applications of the Fisher’s Exact Test

Statistical Analysis