哪位大侠知道M-M2005性别工资差异的分解在stata中实现，help后出现以下：Example without sample selection correction
        . mmsel y x1 x2 x3 x4, group(female) filename(foo) reps(100) pooled

Example with sample selection correction

        . mmsel y x1 x2 x3 x4, group(female) grponlysel single(z1 z2 z3)
            filename(foo) reps(100) pooled adjust(Ps1) reduced(x1 x3)
            cons(x2=1&x4<56|x2=0&x4<24)
哪位做过这方面论文的帮忙介绍下这里面变量的含义和具体如何应用？不甚感激！！！