Frequencies for first 10,000 rows of prostrat variable in namcs1995 dataset :

   provider |
    stratum |
     marker |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,564       35.64       35.64
          2 |      3,616       36.16       71.80
          3 |      2,820       28.20      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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