American Board of Surgery Qualifying Exam (ABS QE) Practice Test 2026 - Free Surgery Exam Practice Questions and Study Guide

Fisher's exact test is specifically designed to be used in situations where sample sizes are small, particularly when the counts in any of the groups are less than 5. This test is most commonly applied in 2x2 contingency tables, which involve categorical data, and it provides a method for determining if there are nonrandom associations between two categorical variables.

When the sample size is small, traditional chi-square tests become unreliable because they rely on the assumption that expected frequencies in each group should ideally be 5 or more. Fisher's exact test, on the other hand, does not make this assumption and is capable of yielding a precise p-value, making it ideal for small sample sizes or when the distribution of the data does not meet the conditions necessary for the use of a chi-square test.

Thus, in clinical research and statistics, Fisher's exact test is intuitively and mathematically appropriate when there are fewer than 5 observations in one of the groups being compared.