Frequencies for first 10,000 rows of stratm variable in nhamcsed1993 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      4,568       45.68       45.68
        202 |      3,430       34.30       79.98
        203 |      1,808       18.08       98.06
        204 |        194        1.94      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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