Frequencies for first 10,000 rows of refer variable in namcs2011 dataset :

   Was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        351        3.51        3.51
       Unknown |        609        6.09        9.60
Not applicable |      7,028       70.28       79.88
           Yes |        721        7.21       87.09
            No |      1,291       12.91      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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