[R-sig-ME] Dispersion parameter in glmmadmb and model selection

Zahwa Al Ayyash (Student) zsa11 at mail.aub.edu
Tue Mar 10 02:39:20 CET 2015

Dear list,

1) I am fitting a negative binomial and zero-inflated negative binomial models using glmmadmb. I am getting a very high dispersion parameter:

Negative binomial dispersion parameter: 403.43 (std. err.: 0.39244)

I am aware that my data might be over-dispersed, but what does the very high value indicate? Could there be an error in estimation?
Also, surprisingly, I am using two different data sets to estimate the neg. bin. models, and I am getting the same value (403.43) but with different std. errors. Any clues?

2) My second question is rather general; What could be the best ways to compare glmmadmb models and select the best amongst Poisson, Neg. Bin, Zero-inflated Poisson, Zero-inflated Neg. Bin., Hurdle Poisson and Hurdle Neg. Bin?

PS: My models employ a random effect to capture correlation among individuals (IDs).

Many thanks to your help,
Zahwa Al-Ayyash

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