heckman lwage educ exper expersq, select(inlf=nwifeinc educ exper expersq age kidslt6 kidsge6) twostep和

heckman lwage educ exper expersq , select(inlf=nwifeinc educ exper  expersq age kidslt6 kidsge6) twostep mills(lambda)

有什么区别呀？第一个命令已经对lambda回归了呀？真心求助！