Frequencies for first 10,000 rows of arrems variable in nhamcsed2011 dataset :

 Arrival by |
  ambulance |      Freq.     Percent        Cum.
------------+-----------------------------------
      Blank |        333        3.33        3.33
    Unknown |        319        3.19        6.52
        Yes |      1,796       17.96       24.48
         No |      7,552       75.52      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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