yan185117462 发表于 2015-3-6 16:27 ![](https://bbs-cdn.datacourse.cn/static/image/common/back.gif)
我也不懂,用xtabond2命令,AR(3)怎么出来的,另外你知道sargan检查过不了怎么办不
Sargan test要求error没有heteroskedasticity。但是,通常panel data 都存在heteroskedasticity,所以在一步robust GMM的时候,Sargan statistic is inconsistent.
Then a theoretically superior overidentifi-cation test for the one-step estimator is that based on the Hansen statistic from a two-step estimate. When the user requests the Sargan test for “robust” one-step GMM regressions, some software packages, including ivreg2 and xtabond2, therefore quietly perform the second GMM step to obtain and report a consistent Hansen statistic.