Frequencies for first 10,000 rows of prostrat variable in namcs1998 dataset :

   provider |
    stratum |
     marker |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,349       23.49       23.49
          2 |      1,802       18.02       41.51
          3 |      2,198       21.98       63.49
          4 |      2,221       22.21       85.70
          5 |      1,218       12.18       97.88
          6 |        212        2.12      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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