Frequencies for fed_aid variable in accident dataset :

Federal-Aid |
     System |      Freq.     Percent        Cum.
------------+-----------------------------------
          2 |        209       36.60       36.60
          3 |        111       19.44       56.04
          4 |        105       18.39       74.43
          5 |        145       25.39       99.82
          9 |          1        0.18      100.00
------------+-----------------------------------
      Total |        571      100.00

by Jean Roth , jroth@nber.org , 18 Apr 2016