Understanding Society User Support

If there a reason why the variables for monthly labour income are not present for the IEMB, even though there is data on earnings?
Output below should clarify that f_fimnlabgrs_dv & f_fimngrs_dv are always -9 for the IEMB, but present for the main sample and for the other pay variables (like f_payg_dv f_payn_dv).

Are there any answered questions on whether f_fimnlabgrs_dv is better/worse than f_payg_dv for measuring earnings???

Thanks,
Steve

. use f_indresp

. su f_fimnlabgrs_dv f_fimngrs_dv f_payg_dv f_payn_dv if f_memorig==1

Variable Obs Mean Std. Dev. Min Max

f_fimnlabg~v 25,885 1215.259 1777.099 -1666.67 15000
f_fimngrs_dv 25,885 1800.833 1772.432 -1666.58 15000
f_payg_dv 25,885 857.4451 1505.202 -9 15000
f_payn_dv 25,885 631.4868 1025.833 -9 15000

. su f_fimnlabgrs_dv f_fimngrs_dv f_payg_dv f_payn_dv if f_memorig==8

Variable Obs Mean Std. Dev. Min Max

f_fimnlabg~v 4,656 -9 0 -9 -9
f_fimngrs_dv 4,656 -9 0 -9 -9
f_payg_dv 4,656 522.7107 1222.099 -9 15000
f_payn_dv 4,656 402.2637 906.403 -9 15000