Frequencies for first 10,000 rows of psum variable in nhamcsopd1994 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,568       55.68       55.68
          2 |      3,614       36.14       91.82
          3 |        818        8.18      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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