流潋 发表于 2013-7-27 21:15 
请问passthru和split有什么作用?
The passthru suboption of gmmstyle() is meaningful only in system GMM, and only for variables for which equation(level) has also been specified. It directs xtabond2 to create instruments for the levels equation that use not the first-differences of the specified variables but the original levels of the same levels be used as instruments. Under the standard assumptions, these instruments are not valid.
The split suboption of gmmstyle() is also meaningful only in system GMM, and then only when neither eq(diff) nor eq(level) is specified. Its sole effect is to split the specified instrument group in two for purposes of difference-in-Sargan/Hansen testing--one instrument set for the transformed equation and one for the levels equation.