- ## data
- data("CigarettesSW")
- CigarettesSW$rprice <- with(CigarettesSW, price/cpi)
- CigarettesSW$rincome <- with(CigarettesSW, income/population/cpi)
- CigarettesSW$tdiff <- with(CigarettesSW, (taxs - tax)/cpi)
-
- ## model
- fm <- ivreg(log(packs) ~ log(rprice) + log(rincome) | log(rincome) + tdiff + I(tax/cpi),
- data = CigarettesSW, subset = year == "1995")
- summary(fm)
- summary(fm, vcov = sandwich, df = Inf, diagnostics = TRUE)
诊断检验部分,给出三个检验:weak instruments(弱工具检验);Dubin-Wu-Hausman(内生解释变量检验);Sargan(工具变量的外生性检验,只有工具变量的个数多于解释变量个数时,才可检验)
Should diagnostic tests for the instrumental-variable regression be carried out? These encompass an F test of the first stage regression for weak instruments, a Wu-Hausman test for endogeneity, and a Sargan test of overidentifying restrictions (only if there are more instruments than regressors).



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