If you specify the keyword MEAN for a categorical variable, PROC SURVEYMEANS estimates the proportion, or relative frequency, for each level of the categorical variable. If you do not specify any statistic-keywords in the PROC SURVEYMEANS statement, the procedure estimates the proportions for levels of the categorical variables, together with their standard errors and confidence limits.

The procedure estimates the proportion in level for variable C as

where is the value of the indicator function for level , defined in the section Definitions and Notation, and equals 1 if the observed value of variable C equals , and equals 0 otherwise. Since the proportion estimator is actually an estimator of the mean for an indicator variable, the procedure computes its variance and standard error according to the method outlined in the section Variance and Standard Error of the Mean. Similarly, the procedure computes confidence limits for proportions as in the section Confidence Limits for the Mean.