Frequencies for first 10,000 rows of workrel variable in nhamcsopd2000 dataset :

             is injury work related? |      Freq.     Percent        Cum.
-------------------------------------+-----------------------------------
                                 Yes |        136        1.36        1.36
                                  No |        348        3.48        4.84
                             Unknown |        511        5.11        9.95
Not applicable (not an injury visit) |      9,005       90.05      100.00
-------------------------------------+-----------------------------------
                               Total |     10,000      100.00

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