Frequencies for fed_aid variable in accident dataset :

Federal-Aid |
     System |      Freq.     Percent        Cum.
------------+-----------------------------------
          2 |        168       34.57       34.57
          3 |         23        4.73       39.30
          4 |         79       16.26       55.56
          5 |         11        2.26       57.82
          6 |          8        1.65       59.47
          7 |         47        9.67       69.14
          8 |        150       30.86      100.00
------------+-----------------------------------
      Total |        486      100.00

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