Frequencies for first 10,000 rows of stratm variable in nhamcsed1997 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      3,384       33.84       33.84
        202 |      2,496       24.96       58.80
        203 |      1,921       19.21       78.01
        204 |      2,199       21.99      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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