Frequencies for haz_inv variable in vehnit dataset :

  HAZARDOUS |
   MATERIAL |
INVOLVEMENT |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      1,272      100.00      100.00
------------+-----------------------------------
      Total |      1,272      100.00

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