Frequencies for first 10,000 rows of prostrat variable in namcs2000 dataset :

   provider |
    stratum |
     marker |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      1,930       19.30       19.30
          2 |      2,346       23.46       42.76
          3 |      2,092       20.92       63.68
          4 |      2,281       22.81       86.49
          5 |      1,351       13.51      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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