library(ivmodel)
data(card.data)
summary(ivmodel(Y=card.data$lwage, D=card.data$educ, Z=card.data$nearc4, X=card.data$exper))
summary(ivmodelFormula(lwage ~ educ + exper | nearc4 + exper, data=card.data))
summary(ivmodel(Y=card.data$lwage, D=card.data$educ, Z=card.data$nearc4))
summary(ivmodelFormula(lwage ~ educ | nearc4, data=card.data))