[R-sig-ME] Emmeans & effects packages: Post-hoc tests for Tweedie glmmTMB model

Millar, Niall n|@||@m|||@r @end|ng |rom w@u@edu
Fri Apr 17 22:51:57 CEST 2020

Are there any problems with using the effects and emmeans packages to interpret glmmTMB models with Tweedie distributions?

I have glmmTMB models using the Tweedie distribution, and I want to draw inference about the direction and magnitude of the predicted effects. In the model given below:

glmmTMB(Shoot.weight ~ Species + N.Level + Rhiz + Species:N.Level + Species:Rhiz + N.Level:Rhiz + N.Level:Rhiz:Species + (1|Block) + (1|Acc), family=tweedie, data=DcleanSOY)

I have a significant effect of the N.Level:Rhiz:Species interaction term (based on a likelihood ratio test). N level is a continuous predictor, and Rhiz and Species are both two-level factors.

I have used the effects package to make a plot with 95% confidence intervals to interpret this 3-way interaction. I have also made separate models for each level of the N level predictor, and used emmeans to get pairwise Tukey contrasts of the Rhiz and Species predictors at each N level.

Can I base my inference on these 95% confidence intervals and/or emmeans contrasts, or are these methods not supported for Tweedie glmmTMB models?

Thanks! -Niall

Niall Millar
PhD Candidate
Porter Lab
School of Biological Sciences

Washington State University Vancouver
14204 NE Salmon Creek Ave
Vancouver, WA  98686
niall.millar using wsu.edu

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