I'm attempting to use lm.cluster in order to produce a linear model with clustered standard errors. However, I've noticed that the output is identical to the same model fitted with an lm() function. Shouldn't the standard errors be larger during clustering? Any help would be appreciated. Below is are my two models:
clustered_model <- lm.cluster(data = data,formula = wageincome ~ aca + state + year_factor + age + (age^2)+ GDP + per_capita_income + unemployment_rate, cluster = "state")
regular_model <- lm(data = data,formula = wageincome ~ aca + state + year_factor + age + (age^2)+ GDP + per_capita_income + unemployment_rate)
Here are the outputs of my two models. Because of the number of coefficients I've only included a sample to illustrate my problem. Here is the clustered output:
term estimate std.error statistic p.value
(Intercept) 84820.96004 10832.85098 7.829975707 4.91E-15
aca -1345.979076 1916.421376 -0.702339837 0.482468403
stateAlaska -6404.573152 12672.62485 -0.505386471 0.613288201
stateArizona -13197.14804 4806.254937 -2.745827721 0.006036602
Here is the output from lm():
term estimate std.error statistic p.value
(Intercept) 84820.96004 10832.85098 7.829975707 4.91E-15
aca -1345.979076 1916.421376 -0.702339837 0.482468403
stateAlaska -6404.573152 12672.62485 -0.505386471 0.613288201
stateArizona -13197.14804 4806.254937 -2.745827721 0.006036602