Frequencies for first 10,000 rows of refer variable in namcs2010 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         blank |        228        2.28        2.28
       unknown |        471        4.71        6.99
not applicable |      7,482       74.82       81.81
           yes |        587        5.87       87.68
            no |      1,232       12.32      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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