Frequencies for first 10,000 rows of arrems variable in nhamcsed2009 dataset :

 arrival by |
  ambulance |      Freq.     Percent        Cum.
------------+-----------------------------------
         -9 |        222        2.22        2.22
         -8 |        264        2.64        4.86
          1 |      1,705       17.05       21.91
          2 |      7,809       78.09      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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