Frequencies for first 10,000 rows of psum variable in nhamcsed1995 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,220       32.20       32.20
          2 |      2,557       25.57       57.77
          3 |      1,878       18.78       76.55
          4 |      2,345       23.45      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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