# Difference between two lmer model

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 .

• @Pavel But I see both have same number of parameter , in first model (Intercept) and Days also , in the second model (Intercept) and Subject.1 Days , though I don't understand what is meant by Subject.1  ? – user81411 Jul 28 '15 at 11:25