Frequencies for first 10,000 rows of refer variable in namcs2007 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         blank |        397        3.97        3.97
       unknown |        503        5.03        9.00
not applicable |      7,409       74.09       83.09
           yes |        565        5.65       88.74
            no |      1,126       11.26      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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