Frequencies for first 10,000 rows of stratm variable in nhamcsed1995 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      3,220       32.20       32.20
        202 |      2,557       25.57       57.77
        203 |      1,878       18.78       76.55
        204 |      2,345       23.45      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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