Frequencies for sch_bus variable in accident dataset :

 School Bus |
    Related |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        486       99.39       99.39
          1 |          3        0.61      100.00
------------+-----------------------------------
      Total |        489      100.00

by Jean Roth , jroth@nber.org , 22 Apr 2016