Frequencies for first 10,000 rows of stratm variable in nhamcsopd1999 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,292       52.92       52.92
        202 |      3,760       37.60       90.52
        203 |        817        8.17       98.69
        204 |        131        1.31      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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