ivreg2 选择项加robust,会显示Kleibergen-Paap Wald F statist
此类判断要参照Stock-Yogo weak ID test临界值,原因:2SLS虽然是一致的,但是有偏的,使用2SLS会带来”显著性水平扭曲“,这种扭曲随着弱工具变量而增大。如果你是名义显著性水平为5%的沃尔德检验,那么在接受真实显著性不超过10%,你可以直接拒绝”弱工具变量“的原假设。
代码如下:
ivreg2 roe (fds= l.fds lfn ) $z yr*, first r
回归结果如下:
First-stage regressions
-----------------------
Warning: collinearities detected among instruments
1st stage tests of excluded exogenous variables may be incorrect
First-stage regression of fds:
Source | SS df MS Number of obs = 798
-------------+---------------------------------- F(16, 781) = 1077.40
Model | 2771.17492 16 173.198433 Prob > F = 0.0000
Residual | 125.55047 781 .160756044 R-squared = 0.9567
-------------+---------------------------------- Adj R-squared = 0.9558
Total | 2896.72539 797 3.63453625 Root MSE = .40094