Frequencies for first 10,000 rows of psum variable in nhamcsed1996 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,982       29.82       29.82
          2 |      2,596       25.96       55.78
          3 |      2,055       20.55       76.33
          4 |      2,367       23.67      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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