# Fisher's exact test for a 2x2 table

## Description

Fisher's exact test in the Calculators menu is used to calculate an exact P-value for a 2x2 frequency table with small number of expected frequencies, for which the Chi-squared test is not appropriate.

## Required input

The data (representing number of cases) for the 2x2 table are entered in the dialog box.

Example: treatment A resulted in 6 successes and 1 failure (6/7 = 85.7%) whereas treatment B resulted in 2 success and 8 failures (2/10 = 20%). The following is entered in the form:

Category 1 | Category 2 | |

Group 1 | 6 | 1 |

Group 2 | 2 | 8 |

The P-value (the probability of obtaining the observed result or a more extreme result) is calculated when you press the Test button.

The result, P=0.015, indicates that the 2 treatments gave significantly different results.

## Interpretation

When the (two-sided) P-value (the probability of obtaining the observed result or a more extreme result) is less than the conventional 0.05, the conclusion is that there is a significant relationship between the two classification factors Group and Category.

## Literature

- Altman DG (1991) Practical statistics for medical research. London: Chapman and Hall.