Frequencies for first 10,000 rows of psum variable in nhamcsopd1999 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,292       52.92       52.92
          2 |      3,760       37.60       90.52
          3 |        817        8.17       98.69
          4 |        131        1.31      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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