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Hello everybody, I have a problem with the the function PVCM in the plm package: I have an unbalanced panel with over 200 companies and 1 to 14 years for each company. I already excluded all NAs: > dataset<-na.omit(dataset) Now I'm trying to fit a variable coefficients model: > model_vc <- pvcm(v1 ~ lag(v2,1), model="within", data=dataset) This results in the following error message: "Fehler in lm.fit(x, y, offset = offset, singular.ok = singular.ok, ...) : 0 (non-NA) cases" I can't figure out what's wrong... Can somebody help me, please? Thanks s...