Frequencies for first 10,000 rows of workrel variable in nhamcsopd1999 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |         93        0.93        0.93
                                  No |        367        3.67        4.60
                             Unknown |        542        5.42       10.02
Not applicable (not an injury visit) |      8,998       89.98      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

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