+ /* To determine whether a case is included in a given table for a particular
+ kind of summary, consider the following charts for each variable in the
+ table. Only if "yes" appears for every variable for the summary is the
+ case counted.
+
+ Categorical variables: VALIDN COUNT TOTALN
+ Valid values in included categories yes yes yes
+ Missing values in included categories --- yes yes
+ Missing values in excluded categories --- --- yes
+ Valid values in excluded categories --- --- ---
+
+ Scale variables: VALIDN COUNT TOTALN
+ Valid value yes yes yes
+ Missing value --- yes yes
+
+ Missing values include both user- and system-missing. (The system-missing
+ value is always in an excluded category.)
+ */