If an observation has a missing value for a response variable, PROC NPAR1WAY excludes that observation from the analysis.

By default, PROC NPAR1WAY excludes observations with missing values of the CLASS variable. If you specify the MISSING option, PROC NPAR1WAY treats missing values of the CLASS variable as a valid class level and includes these observations in the analysis.

PROC NPAR1WAY treats missing BY variable values like any other BY variable value. The missing values form a separate BY group. When a value of the FREQ variable is missing, PROC NPAR1WAY excludes the observation from the analysis.