Exact Testing Procedures in SAS

In categorical data analysis, the majority of methods are based on asymptotic approaches. As we all know, asymptotic approaches are very easy to calculate, however, they may have an unsatisfied type I error control. Actual type I error rates of testing procedures could be underestimated or over-estimated for the discrete data. In addition, when power of the study is overestimated, sample size is definitely under-estimated. The sample size in a study is actually not enough to attain the pre-specified power. In order to avoid such problems, exact approaches can be considered as alternatives in data analysis. SAS provides the option EXACT in several procedures for producing exact p-values as well as exact confidence intervals. We will review the commonly used conditional exact approach (Fisher’s test) by using examples in the SAS help files. We will also compare the EXACT statement in SAS to exact testing procedures in other statistical software packages.