Frequencies for first 10,000 rows of stratm variable in nhamcsopd2001 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      7,139       71.39       71.39
        202 |      2,420       24.20       95.59
        203 |        441        4.41      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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