求问……endogenous treatment assignment和 endogenous covariates有什么区别呢？

stata 对于这两种情况用了不同发语句……所以很好奇这两种情况具体怎么区分，求大神解答
Basic interval regression with endogenous covariates

eintreg depvar_1 depvar_2 [indepvars], endogenous(depvars_en =
                varlist_en) [options]


Basic interval regress with endogenous treatment assignment

        eintreg depvar_1 depvar_2 [indepvars], entreat(depvar_tr [=
                varlist_tr]) [options]