proc format;
value answer 1='yes'
             2='no'
             3='unclear';
run;
proc format cntlout=fmtout;
  select answer;
run;

proc sql noprint;
   select count(distinct label) into : n
    from fmtout
        where fmtname="ANSWER" and type="N";
quit;

%put &n;

谢谢pobel！如有更简单实现的方法，可以另给论坛币！