Frequencies for ptrailer variable in parkwork dataset :

    Vehicle |
   Trailing |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |        902       90.02       90.02
          1 |         91        9.08       99.10
          2 |          2        0.20       99.30
          5 |          4        0.40       99.70
          6 |          2        0.20       99.90
          9 |          1        0.10      100.00
------------+-----------------------------------
      Total |      1,002      100.00

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