Frequencies for first 10,000 rows of refer variable in namcs2004 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        724        7.24        7.24
           Yes |      2,253       22.53       29.77
            No |      3,473       34.73       64.50
       Unknown |        606        6.06       70.56
Not applicable |      2,944       29.44      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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