Frequencies for first 10,000 rows of stratm variable in nhamcsed2001 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,283       52.83       52.83
        202 |      3,626       36.26       89.09
        203 |        768        7.68       96.77
        204 |        323        3.23      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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