How does one go about including country-pair fixed effects in plm package regressions (OLS, RE, FE, and Hausman-Taylor estimators)? I am hoping to use plm because it is very easy and I'm baby-new to R. I have received the following code from a kind professor who I don't actually know: pairid <- paste(isoex,isoim) isoexyear <- paste(isoex,year) isoimyear <- paste(isoim,year) # do not worry about the other variables, focus on the G() portion which is using Pair FE, exporter-year, and importer-year felm(ln_trade~bc_o + l_bc_o + bc_d + l_bc_d + G(pairid) + G(isoexyear) + G(isoimyear), clustervar=as.factor(pairid), data=gravity_data) I have no idea how to implement that code at all and figure there has to be some simpler way than using a complicated method in felm. Be well. I appreciate your time. [[alternative HTML version deleted]]