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I am rather new to R. I am trying to run a GLMM - binomial logit.

I have three independent variables (x1, x2, x3) and a dependent variable (y) - all numeric.

m <-glmer(y ~ x1:x2:x3 + (1 | participant), data=mydata, family=binomial)
  1. How can I check for the model's assumptions?
  2. Which model can be appropriate in case the assumptions are not met?

Your help is much appreciated!

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2 Answers 2

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For a binomial glmm, the main assumptions are:

  • the outcome/response is binary. You said the variables including y are "all numeric"
  • the random effects are approximately normally distrubuted. The main thing here is that you have sufficient number of participants for the software to reliably estimate a variance.
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  • $\begingroup$ Does this answer your question ? If so, please consider marking it as accepted. Thanks ! $\endgroup$
    – Robert Long
    Commented Jul 19, 2020 at 4:47
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In terms of model misspecification and the assumptions regarding the distribution of the residuals, GLMM is a bit problematic compared to LMM because in the binomial case the residuals are stacked on 0 and 1. The DHARMa package in R offers the solution by using a simulation-based approach to check for the GLMM residual distribution and plot tests for normality, uniformity, and dispersion. Check it out https://cran.r-project.org/web/packages/DHARMa/vignettes/DHARMa.html For model comparison, you can use bootstrapped likelihood values and choose the best model accordingly https://rpubs.com/hughes/22059.

Also, for more info on GLMM, I advise you to see https://bbolker.github.io/mixedmodels-misc/ecostats_chap.html

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