Try a different example: set.seed(123) N <- 24 k <- 6 x <- 1:N f <- rep(rnorm(k, 0, 4), each = N/k) e <- rnorm(N) y <- x + f + e fac <- gl(k, N/k) library(lme4) fm1 <- lmer(y ~ x + (1|fac)); fm1 fm0 <- lmer(y ~ x -1 + (1|fac)); fm0 plot(y, fitted(fm0)) abline(a = 0, b = 1, lty = 2, col = "blue")