Frequencies for prev_dwi variable in vehicle dataset :

   PREVIOUS |
        DWI |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        670       93.58       93.58
          1 |          1        0.14       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