[R-sig-ME] Cook's distance: glmmADMB ZIP / influence.ME not compatible?

[Ashley Asmus]

Dear r-sig-ME,

I am working with a small (zero-inflated) dataset of counts. The design is
repeated-measures, with several measures at each time point made in
experimental blocks. I have fit the model with glmmADMB using the
zero-inflated poisson options:

zip<-glmmadmb(wasp~ treatment  +  (1|sample.period) + (1|block), data=data,
family="poisson", zeroInflation=TRUE)

I am suspicious of 1-3 observations (the dataset is only 24 observations
big, so I promise to be cautious), and wish to evaluate their influence on
the model fit. Usually I work in lme4, then use the influence.ME package
and eliminate points based on cook's distance/leverage plots. Applying
influence.ME to the glmmADMB model produces a strange error message:

library(influence.ME)
infl <- influence(zip, obs = TRUE)
Error in eval(expr, envir, enclos) : object 'sample.period' not found

For some reason influence.ME is not finding my random factor
"sample.period." Are glmmADMB and influence.ME incompatible when
zero-inflation models are involved? If anyone knows of an alternative
approach I would love to hear about it.

Thank you very much!
Ashley Asmus
Ph.D. Student
The University of Texas at Arlington

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