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lme4 and nlme are R packages used for fitting linear, generalized linear and nonlinear mixed effects models. For general questions about mixed models use [mixed-model] tag.

6 votes

Variance-covariance structure for random-effects in lme4

I can show this by example. Covariance terms are specified in the same formula as the fixed and random effects. Covariance terms are specified by the way the formula is written. For example: glmer( …
ndoogan's user avatar
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3 votes

Lmer model design

I think your specification is fine. I'm not so sure you'll end up needing to let every single slope vary randomly, but it's a start I suppose. One thing you might want to try is allowing the random e …
ndoogan's user avatar
  • 1,358
3 votes

Big disagreement in the slope estimate when groups are treated as random vs. fixed in a mixe...

After considerable contemplation, I believe I have discovered my own answer. I believe an econometrician would define my independent variable to be endogenous and thus be correlated with both independ …
ndoogan's user avatar
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1 vote

How do I setup a model with hierarchical structure using lmer in R?

Preface There is a discrepancy in your output. You do not allow $TL$ slope to vary according to the output for model 2, which could explain the difference in AIC if that additional error term doesn't …
ndoogan's user avatar
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4 votes

How to test for overdispersion in Poisson GLMM with lmer() in R?

Among many other useful tidbits on GLMM with lmer() and other GLMM fitting software, check out the section on the following web page called How can I deal with overdispersion in GLMMs? http://glmm.wi …
ndoogan's user avatar
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21 votes
2 answers
4k views

Big disagreement in the slope estimate when groups are treated as random vs. fixed in a mixe...

I understand that we use random effects (or mixed effects) models when we believe that some model parameter(s) vary randomly across some grouping factor. I have a desire to fit a model where the respo …
ndoogan's user avatar
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6 votes
Accepted

Correct interpretation of Lmer output

I address your interpretations 1 and 2 in order: 1) How you interpret factors depends on which level of the factor is the reference category. The fact that the model calls it Type2 suggests to me tha …
ndoogan's user avatar
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