Frequencies for first 10,000 rows of stratm variable in nhamcsopd1992 dataset :

PSU stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      6,251       62.51       62.51
        202 |      2,450       24.50       87.01
        203 |        666        6.66       93.67
        204 |        633        6.33      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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