Frequencies for first 10,000 rows of stratm variable in nhamcsopd1998 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
        201 |      5,937       59.37       59.37
        202 |      3,095       30.95       90.32
        203 |        968        9.68      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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