Frequencies for first 10,000 rows of workrel variable in nhamcsed2001 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |        326        3.26        3.26
                                  No |      2,254       22.54       25.80
                             Unknown |      1,110       11.10       36.90
Not applicable (not an injury visit) |      6,310       63.10      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

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