Frequencies for first 10,000 rows of stratm variable in nhamcsed1996 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      2,982       29.82       29.82
        202 |      2,596       25.96       55.78
        203 |      2,055       20.55       76.33
        204 |      2,367       23.67      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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