Frequencies for first 10,000 rows of poppsum variable in namcs2002 dataset :

    Stratum |
  counts of |
       PSUs |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |      5,559       55.59       55.59
          1 |      4,441       44.41      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016