Frequencies for first 10,000 rows of psum variable in nhamcsopd1993 dataset :

 psu marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,623       56.23       56.23
          2 |      3,569       35.69       91.92
          3 |        808        8.08      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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