Can you please explain where is the difference between the following two models :
fm1 <- lmer(Reaction ~ Days + (Days | Subject), sleepstudy) fm2 <- lmer(Reaction ~ Days + (1|Subject) + (0+Days|Subject), sleepstudy)
I noticed there is some discrepency in the estimate for random effect between model fm1 and fm2 . But don't know why ?
summary(fm1)$varcor Groups Name Std.Dev. Corr Subject (Intercept) 24.7404 Days 5.9221 0.066 Residual 25.5918 summary(fm2)$varcor Groups Name Std.Dev. Subject (Intercept) 25.0513 Subject.1 Days 5.9882 Residual 25.5653
And the fixed effect estimates are same for the both model .