Frequencies for phaz_id variable in parkwork dataset :

  hazardous |
  materials |
involvement |
  /placard- |
        hm3 |
identificat |
 ion number |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      1,142       99.65       99.65
       1993 |          1        0.09       99.74
       8888 |          3        0.26      100.00
------------+-----------------------------------
      Total |      1,146      100.00

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