Frequencies for first 10,000 rows of psum variable in nhamcsed2002 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      6,032       60.32       60.32
          2 |      2,932       29.32       89.64
          3 |        820        8.20       97.84
          4 |        216        2.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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