I am using a binomial GLMM and am confused on how to test for homoscedasticity of residuals. When I use normal difference residuals it shows heteroscedasticity, but when I use pearsons residuals it shows more of a homoscedastic trend. I don’t know how to use deviance residuals, but red that ppc_ch…

You might find this thread useful: [image] Differing posterior predictive checks for logistic binomial model with and without addition-terms brms Hi all, Not so much an issue as double-checking expected behaviour: I’m fitting a logistic binomial model where the response …

Wow this response was very helpful thanks @jsocolar Ok so when checking for (over or under- ) dispersion the posterior predictive check can give you insight into this based on how the predictions are distributed around your observed values. So my follow up question is if your model is showing more…

Under-dispersion is not the same thing as predicted values tending to be lower than observed values. Under-dispersion is if predicted values tend to be more variable than observed values (the observed values are under-dispersed compared to binomial sampling). If you are seeing a clear systematic te…

Binomial Logistic GLMM [image] Binary Logistic GLMM [image] These are my posterior predictive checks. So would these indicate over-dispersion? @jsocolar

These plots contain no indication of misspecification, but they are not the most sensitive tests for over- or under-dispersion.

@jsocolar What test would you recommend for under or over-dispersion?

If you’re interested in logistic regression from a residual perspective, Roback and Legler cover that in chapter 6 . From a pp-check perspective, those plots look spectacular.

@Solomon Thanks for the reference. Would you recommend any other sources for testing model assumptions and understanding different pp_checks. Also @Solomon I would really appreciate it if I could get your input on this question. Plotting Interaction for Binomial GLMM Multi-Membership Model - Int…

You’re asking a big question, which requires a similarly big answer. Consider this book, Statistical Rethinking | Richard McElreath , and its related lecture series, https://www.youtube.com/@rmcelreath/playlists . I can’t overstate how big of a change it is to move away from a conventional ‘test the r…

As to the link you provided, I’m not experienced with mult-membership, so I’ll have to let others chip in.

Binomial GLMM Assumptions

Interfaces brms

isabelaruelas January 27, 2026, 11:01pm 13

Hello! By any chance, do you have any papers or resources that explain why we don’t check for homoscedasticity in binomial models and what the proper diagnostics are?

Topic		Replies	Views
Modeling heteroskedasticity using the auxiliary parameter phi for beta_binomial distribution brms techniques , fitting-issues , stan , hierarchical-model , brms	13	1295	February 13, 2023
Underdispersed binomial/overdispersed beta-binomial Modeling	0	569	December 21, 2022
Posterior predictive check for binomial regression General	3	2699	January 24, 2019
Dispersion and binomial vs beta-binomial Modeling	6	1555	January 4, 2023
Posterior predictive check looks weird - what can I do? Modeling posterior-predictive , brms	16	4554	April 24, 2024

Binomial GLMM Assumptions

Related topics