This chapter introduces a group of statistical tests to analyze qualitative variables. The chi-square is a robust, nonparametric test that evaluates whether there is a relationship between two categorical variables at a nominal level. Its formula, calculation, assumptions, and interpretation are explained. Fisher's exact test, another test used to evaluate the association of categorical data and preferred when the sample size is smaller, is described in this review. Mantel–Haenszel, a variation of the chi-square test, used in observational studies, is also discussed.