Frequencies for first 10,000 rows of psum variable in nhamcsed2000 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,958       39.58       39.58
          2 |      2,901       29.01       68.59
          3 |      2,174       21.74       90.33
          4 |        967        9.67      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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