Frequencies for first 10,000 rows of psum variable in nhamcsopd1996 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,781       57.81       57.81
          2 |      3,390       33.90       91.71
          3 |        712        7.12       98.83
          4 |        117        1.17      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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