Frequencies for first 10,000 rows of psum variable in nhamcsopd2002 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      6,743       67.43       67.43
          2 |      2,133       21.33       88.76
          3 |      1,124       11.24      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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