Frequencies for first 10,000 rows of haz_id variable in vehicle dataset :

  hazardous |
  materials |
involvement |
  /placard- |
        hm3 |
identificat |
 ion number |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,983       99.83       99.83
       1203 |          8        0.08       99.91
       1267 |          1        0.01       99.92
       1863 |          1        0.01       99.93
       1972 |          1        0.01       99.94
       1987 |          1        0.01       99.95
       3077 |          1        0.01       99.96
       3266 |          1        0.01       99.97
       8888 |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Oct 2016