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

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,937       59.37       59.37
          2 |      3,095       30.95       90.32
          3 |        968        9.68      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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