Ex1(ctd) The estimate of B,,is the return to education,but can it be considered causal? While the error term,u,includes other factors affecting earnings,want to control for as much as possible Some things are still unobserved,which correlates with education.It remains to be problematic. ◆cf Angrist(1991) Econometrics 15-Zhuxi 11Econometrics 15 - Zhuxi 11 Ex1 (ctd) The estimate of 1 , is the return to education, but can it be considered causal? While the error term, u, includes other factors affecting earnings, want to control for as much as possible Some things are still unobserved, which correlates with education. It remains to be problematic. cf Angrist(1991)