Dear plm Package users, I use the plm package a lot but I have not updated it for some times. Now I realized the following difficulty with the summary.plm function (demonstrated with the example from the ?plm documentation). library(plm) data("Produc", package="Ecdat") estimation_method<-"within" estimation_effect<-"individual" zz <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp, data=Produc, index=c("state","year") , method=estimation_method , effect=estimation_effect ) summary(zz) Error: object of type 'symbol' is not subsettable But if I run zz <- plm(log(gsp)~log(pcap)+log(pc)+log(emp)+unemp, data=Produc, index=c("state","year") , method="within" , effect="individual" ) summary(zz) the summary function works fine. Is it wrong (or bad practice) to define the function's parameters as I did in the upper example? If yes, how should it be done correctly such that the summary function works? I am running R 2.8.1 wie plm versin 1.1-1 on a Windows XP workstation. Thank you for your advice, Ulrich Morawetz [[alternative HTML version deleted]]