[R-sig-ME] lmer vs. nlme

[Ashley Cohen]

Hi Mixed Models group;



I was wondering if you might be able to clarify some confusion I am having
with results from lmer.



I am running a mixed model with fixed effects for treatment, time and an
interaction between treatment and time. A random effect has been added in
for subject (for repeated measures).



I was under the impression, based on the response from Ben Bolker here,
that lmer would be estimating an unstructured correlation matrix:

http://stats.stackexchange.com/questions/86958/variance-covariance-structure-for-random-effects-in-glmer



However, when I ran the model with lme, specifying a compound symmetric
correlation structure and random effect, I got the exact same results as
from lmer.



I am not sure about what is going on and was wondering if you had any
thoughts on this. I also couldn’t find a way to pull out the correlation
matrix from lmer.



Thank you,


Ashley

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