Frequencies for first 10,000 rows of stratm variable in nhamcsopd1994 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,568       55.68       55.68
        202 |      3,614       36.14       91.82
        203 |        818        8.18      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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