[R-sig-ME] Question about random effects variance in lme4

[Chiara Masci]

Good morning,

I am a researcher at the Department of Mathematics of Politecnico di Milano, Italy.
I am working in the field of parametric and non parametric mixed-effects models and I would like to ask a question about the computation of random effects in the R package lme4.


If possible, I would like to ask a clarification about the random effects variance: I understand how the conditional variances of random effects are computed and then displayed by means of ranef and dotplot functions.  What I did not get is how the condVar values in ranef are related to the random effects variance that I can read from the summary of the lmer model (or, equivalently, from the function varCorr(lmer model)). I see that, if groups have the same number of observations within them, the values of condVar are all the same, so I guess they depend somehow on the number of observations. I am missing the relation between the group- specific condiational variances and the overall variance of random effects.


Thank you very much!

Best wishes,
Chiara Masci

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