Hello, I am trying to predict using a fixed effects model on an unbalanced panel. I tried using the code in the example but the fitted values I get are very different from the fitted values using observed value - residual. I am giving my code snippet here: train_data <- na.omit(read.csv(file="usersessions-with-char-sec-train-subset-100.csv", header=TRUE, row.names = NULL, sep="|")) panel.data.train <- plm.data(train_data, index = c("session_start","userid")) mdl_fe <-plm(session_length~age+session_length_mvavg, data panel.data.train, model = "within") ##Summaries summary(mdl_fe) fixefs <- fixef(mdl_fe)[index(mdl_fe, which = "userid")] fit_hand <- fixefs + mdl_fe$coefficients[1] * panel.data.train$age + mdl_fe$coefficients[2] * panel.data.train$session_length_mvavg fitval <- panel.data.train$session_length-mdl_fe$residuals Also when I tried the prediction function from the prediction package, I get the following error: Error in crossprod(beta, t(X)) : non-conformable arguments Any help is appreciated. Thanks! Jayashree