Frequencies for first 10,000 rows of psum variable in nhamcsopd2000 dataset :

psu stratum |
     marker |
   (masked) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,264       52.64       52.64
          2 |      3,959       39.59       92.23
          3 |        660        6.60       98.83
          4 |        117        1.17      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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