library(AER) data(CPS1985) dummy_mod <- lm(wage ~ gender, data = CPS1985) # test whether the gender gap is significantly different from zero # use robust standard errors coeftest(dummy_mod, vcov. = vcovHC, type = "HC0") # or linearHypothesis(dummy_mod, "genderfemale=0", vcov. = vcovHC, type = "HC0") test_predefined_objects("dummy_mod") test_or({ test_function("coeftest", args = c("x", "vcov.")) },{ test_function("linearHypothesis", args = c("model", "vcov.", "hypothesis.matrix")) },{ test_function("linearHypothesis", args = c("model", "hypothesis.matrix", "type")) }) success_msg("Right! The hypothesis that there is no wage gap is rejected at any common level.")