Linked Questions

18
votes
2answers
8k views

Random effect equal to 0 in generalized linear mixed model [duplicate]

Sorry if I'm missing something very obvious here but I am new to mixed effect modelling. I am trying to model a binomial presence/absence response as a function of percentages of habitat within the ...
34
votes
3answers
45k views

How can I test whether a random effect is significant?

I am trying to understand when to use a random effect and when it is unnecessary. Ive been told a rule of thumb is if you have 4 or more groups/individuals which I do (15 individual moose). Some of ...
9
votes
3answers
4k views

What to do with random effects correlation that equals 1 or -1?

Not so uncommon occurrence when dealing with complex maximal mixed models (estimating all possible random effects for given data and model) is perfect (+1 or -1) or nearly perfect correlation among ...
3
votes
0answers
2k views

Singular fit with simplest random structure in lmer (lme4), is a Bayesian approach the only option?

I'm running a mixed model with the lmer function from the lme4 package in R and ran into some issues with singular fits. I get the warning message 'singular fit', ...
5
votes
2answers
133 views

Don't understand why glmm random effect variance is zero. Have reviewed similar questions still dont get it

I study a colonially-nesting bird species. I am trying to perform an AICc evaluation of GLMMs for a nest site selection study. I collected data at nest sites and paired random sites. I want to ...
2
votes
1answer
644 views

Why are the coefficients of REML and ML estimation the same? What does that mean?

I have estimated a linear mixed model with REML and ML estimation. However, the estimated coefficients do not differ. The standard errors of the coefficients are slightly higher for the REML ...
3
votes
0answers
327 views

Instability in glmer model at zero random effect variance

I am getting very different results from glmer (using version 0.999375.37 of lme4) when running in different environments (I can't pinpoint the source of discrepancy, but let's assume some floating ...
3
votes
1answer
127 views

variance-covariance matrix with negative entries on mixed model fit

I am fitting a linear mixed effect model in R (function lme), and I get a Var-Cov matrix with negative entries (Log-Cholesky). This does not allow me to compute confidence intervals on the standard ...
2
votes
0answers
204 views

Non-zero random slope variance in lmer for predictor that is constant inside each level of the grouping variable

If I run a mixed model including a level 2 predictor as a random slope, it is sometimes possible to get an estimation of the variance. For example: ...
1
vote
1answer
144 views

Zero random intercept variance for glmer mixed model

I'm running the following glmer model in lme4: ...
2
votes
0answers
129 views

Zero variance of random effects after removing of correlation in linear mixed models

I have some hierarchical data (roughly 23 observations per individual, 20 individuals per region, and 17 regions in total), and use linear mixed models (LMM) to adjust for the dependencies that come ...
0
votes
0answers
15 views

mixed model has -1 or 1 in the random effect correlation matrix or 0 in the random effect covariance matrix

In the linear mixed model, when we fit the model using lmer in the lme4 package in R, we ...