Frequencies for first 10,000 rows of psum variable in nhamcsopd2001 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      7,139       71.39       71.39
          2 |      2,420       24.20       95.59
          3 |        441        4.41      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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