When you specify the CHISQ option in the TABLES statement, PROC FREQ performs the following chi-square tests for each two-way table: Pearson chi-square, continuity-adjusted chi-square for 2 ×2 tables, ...

and that this follows a chi-squared distribution with (rows-1)*(columns-1) degrees of freedom under the null hypothesis, where rows and columns refer to the number of rows and columns in the ...

The chi-square value is calculated using the following formula: Using this formula, the difference between the observed and expected frequencies is calculated for each experimental outcome category.