Look at the Data Summary Table. Most likely, including the CLASS statement decreases the Number of Observations count. Missing class levels are excluded from analysis, even if they are not part of the model.
Example:
data classMissing12;
set sashelp.class;
if age=12 then call missing(age);
run;
proc surveyreg data=classMissing12;
class age;
model weight = height / solution;
run;
proc surveyreg data=classMissing12;
*class age;
model weight = height / solution;
run;
... View more
