Frequencies for first 10,000 rows of psum variable in nhamcsed1998 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      4,502       45.02       45.02
          2 |      2,373       23.73       68.75
          3 |      2,357       23.57       92.32
          4 |        768        7.68      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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