Frequencies for first 10,000 rows of psum variable in nhamcsed1999 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,090       30.90       30.90
          2 |      2,539       25.39       56.29
          3 |      2,014       20.14       76.43
          4 |      2,357       23.57      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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