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varIdent in glmmTMB?

2 messages · Davide Nespoli, Ben Bolker

Original
Davide Nespoli
# 
Dear development team,

this is Davide Nespoli, researcher at the University of Florence (Italy).
After building a zero-inflated negative binomial GLMM of the form:

m<-glmmTMB(Time~Temperature*Sex+Position+(1|Individual),family=nbinom1(),
ziformula=~1, data=Perm)

I have a good model, but with a bit of heteroschedasticity due to the
different levels of Temperature (which is a 3-level factor).
I am wondering if it is possible to integrate a varIdent covariance
structure in the model.
I have already tried
"+(1|Temperature), dispformula=~0,"
but it doesn't work (neither for ZINB nor for ordered beta on proportional
data).
Is there a way to integrate it in such a model in glmmTMB?

Thank you very much.
Best regards,



--
Davide Nespoli, PhD
Department of Biology
University of Florence
via Madonna del Piano 6, I-50019
Sesto Fiorentino (FI), Italy
email: davide.nespoli at unifi.it
Tel. +390554574722
Ben Bolker
# 
The glmmTMB analogue of varIdent(form = ~ Temperature) would be

dispformula = ~ Temperature

   or (if you want the variance model to be parameterized as a 
log-dispersion for each temperature rather than a log-dispersion for the 
first temperature level plus differences in log-dispersion)

   dispformula = ~ 0 + Temperature

   cheers
    Ben Bolker
On 2025-01-14 7:14 a.m., Davide Nespoli wrote: