Frequencies for first 10,000 rows of prostrat variable in namcs1994 dataset :

   provider |
    stratum |
     marker |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,010       30.10       30.10
          2 |      3,361       33.61       63.71
          3 |      2,869       28.69       92.40
          4 |        760        7.60      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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