Frequencies for first 10,000 rows of refer variable in namcs2009 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         blank |        310        3.10        3.10
       unknown |        599        5.99        9.09
not applicable |      7,684       76.84       85.93
           yes |        444        4.44       90.37
            no |        963        9.63      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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