Frequencies for first 10,000 rows of stratm variable in nhamcsopd2000 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,264       52.64       52.64
        202 |      3,959       39.59       92.23
        203 |        660        6.60       98.83
        204 |        117        1.17      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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