data SAMPLE (drop = k n) ;
      retain k 100 n;
      if _n_ = 1 then n = total;
      do i = 1 to total;
         if ranuni(0) <= k / n then do;
            set POP nobs = total point = i;
            output;
            k = k - 1;
         end;
         n = n - 1;
         if k = 0 then stop;
      end;
   run;