Frequencies for first 10,000 rows of workrel variable in nhamcsopd1997 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |         98        0.98        0.98
                                  No |        373        3.73        4.71
                             Unknown |        486        4.86        9.57
Not applicable (not an injury visit) |      9,043       90.43      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016