Please help, I have a strange problem. I've got a balanced panel data set. I use dummy variable regression and I've got results with lm function. summary(lm(y ~ post + t19961 + t19962 + t19963 + t19964 + t19971 + t19972 + t19973 + t19974 + t19981+factor( id))) The problem is that I would like to get my standard errors clustered but then gets the following error message: f<-(lm(y ~ post + t19961 + t19962 + t19963 + t19964 + t19971 + t19972 + t19973 + t19974 + t19981+factor( id))) library(Design) g.clust1 <- robcov(f, id) Error in match.arg(type) : 'arg' should be one of working, response, deviance, pearson, partial All my variables is vectors and I've tried with other variables inside and outside the model and all results in the same errormessage. Best regards Anders Eklund Stockholm, Sweden.