Frequencies for prev_spd variable in vehicle dataset :

   PREVIOUS |
   SPEEDING |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        635       88.69       88.69
          1 |         30        4.19       92.88
          2 |          6        0.84       93.72
         99 |         42        5.87       99.58
          . |          3        0.42      100.00
------------+-----------------------------------
      Total |        716      100.00

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