Frequencies for first 10,000 rows of psum variable in nhamcsed1997 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,384       33.84       33.84
          2 |      2,496       24.96       58.80
          3 |      1,921       19.21       78.01
          4 |      2,199       21.99      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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