Frequencies for first 10,000 rows of psum variable in nhamcsopd1992 dataset :

 PSU marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      6,251       62.51       62.51
          2 |      2,450       24.50       87.01
          3 |        666        6.66       93.67
          4 |        633        6.33      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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