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Generalised Linear Mixed Model Diagnostics using DHARMa

I am running a GLMM in R in lme4 package, the outcome variable is binary and the 10 fixed effects are a mix of categorical and continuous variables. The models have three random-effects.
I am using DHARMa to check for the GLMM assumptions.

simulateResiduals(fittedModel = cm5, asFactor=T, plot = T, quantreg=T,1000)
It doesn’t show that I have big misspecification problems however the residuals are not uniform, and the KS-test and the dispersion test is significant.
Model with continuous fixed effects

I recalculate the residuals at each random effect levels and gave the same issues.
I ran the same model but this time I categorised all the continuous fixed effects, the DRAHMa output is much better and better meet the assumptions.
Model with categorised fixed effects

I am not a fan of categorising continuous variables and I don’t want to lose information to meet the assumptions. But at the same time, I don’t want biased estimates because of not meeting the assumptions.
Please advise, which option to sacrifice.
Thank you

Cross Validated Asked by AhmadMkhatib on November 21, 2021

1 Answers

One Answer

I'm the developer of DHARMa - from what I see, the deviations are minimal, so I would not be worried about the significant p-values. You just have a lot of data, so even a minimal deviation will become significant (this is also discussed in the help / vignette).

What would be more interesting is probably to plot residuals agains predictors. If you see no patterns there, you should be fine.

Answered by Florian Hartig on November 21, 2021

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