Frequencies for first 10,000 rows of refer variable in namcs2005 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        299        2.99        2.99
           Yes |        731        7.31       10.30
            No |        970        9.70       20.00
       Unknown |        316        3.16       23.16
Not applicable |      7,684       76.84      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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