Frequencies for first 10,000 rows of workrel variable in nhamcsed1999 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |        345        3.45        3.45
                                  No |      1,990       19.90       23.35
                             Unknown |      1,124       11.24       34.59
Not applicable (not an injury visit) |      6,541       65.41      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

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