hello everyone I am currently working on an unbalanced data, and i want to test "twoways" effect, I know that for the unbalanced data random, twoways doenst work, but fixed twoways supposed to work, but it doesnt and when i enter the following model i have an error which i couldnt understand why. Because the same model and same command with the same data set works perfectly with another computer but doesnt work with my computer. Does anyone of you have any idea, what could be the reason for this error? here is the basic model that i am using newdata = plm.data(ds,index=c("stno","year")) dsn1<-plm(lnQ~lnC+lnL+lnM+lnE+eco+RD,data=newdata,effect="twoways",model="within") but i have this error: Error in rep.int(c(1, numeric(n)), n - 1L) : negative length vectors are not allowed thank your for your help in advance Serdal -- Serdal Ozusaglam [[alternative HTML version deleted]]