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

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,781       57.81       57.81
        202 |      3,390       33.90       91.71
        203 |        712        7.12       98.83
        204 |        117        1.17      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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