Frequencies for first 10,000 rows of refer variable in namcs2001 dataset :

   was patient |
  referred for |
   this visit? |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |        745        7.45        7.45
           Yes |      2,449       24.49       31.94
            No |      3,300       33.00       64.94
       Unknown |        595        5.95       70.89
Not applicable |      2,911       29.11      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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