Frequencies for first 10,000 rows of refer variable in namcs2014 dataset :

   Was patient |
  referred for |
        visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        162        1.62        1.62
       Unknown |        971        9.71       11.33
Not applicable |      3,858       38.58       49.91
           Yes |      1,981       19.81       69.72
            No |      3,028       30.28      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 27 Mar 2017