大神们好,我用xtabond2命令做的回归,二阶相关检验Arellano-Bond test for AR(2) in first differences不通过,应该怎么调,问题出在哪里了?急,谢谢各位!调工具变量的个数也不行。obs=4123,group=102
xtabond2 cs l.cs ///
riskpremium1 hml1 smb1 ///
time1-time7 ind1-ind9 irtype_1-irtype_2 region_1-region_4 , ///
gmm(cs, lag(2 3)) ///
iv(time1-time7 ind1-ind9 irtype_1-irtype_2 region_1-region_4) ///
robust