Frequencies for first 10,000 rows of workrel variable in nhamcsed1998 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |        388        3.88        3.88
                                  No |      1,932       19.32       23.20
                             Unknown |      1,075       10.75       33.95
Not applicable (not an injury visit) |      6,605       66.05      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

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