Frequencies for first 10,000 rows of stratm variable in nhamcsopd1993 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,623       56.23       56.23
        202 |      3,569       35.69       91.92
        203 |        808        8.08      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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