Frequencies for first 10,000 rows of poppsum variable in namcs1996 dataset :

    stratum |
  counts of |
       psus |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |      5,310       53.10       53.10
          1 |      4,690       46.90      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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