Frequencies for first 10,000 rows of refer variable in namcs2002 dataset :

   Was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        591        5.91        5.91
           Yes |      2,120       21.20       27.11
            No |      3,244       32.44       59.55
       Unknown |        537        5.37       64.92
Not applicable |      3,508       35.08      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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