Frequencies for first 10,000 rows of arrems variable in nhamcsed2013 dataset :

 Arrival by |
  ambulance |      Freq.     Percent        Cum.
------------+-----------------------------------
      Blank |        186        1.86        1.86
    Unknown |        404        4.04        5.90
        Yes |      1,697       16.97       22.87
         No |      7,713       77.13      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 7 Nov 2016