[R-sig-ME] glmmTMB: Get phi from dispersion model

m@tthi@s@suter m@iii@g oii @groscope@@dmi@@ch m@tthi@s@suter m@iii@g oii @groscope@@dmi@@ch
Wed Jan 13 09:16:45 CET 2021

When fitting a negative binomial model in glmmTMB() using "family=nbinom2", but without specifying the dispersion model, the summary() gives an estimate for the dispersion parameter as "Overdispersion parameter for nbinom2 family (): XX", which represents - as far I understand - the phi value described in the manual (also termed theta in other environments).

If a dispersion model is specified with "dispformula=~ ...", the summary() gives the estimates for the "Dispersion model". How do these relate to the phi value? I read in the manual that "phi=exp(eta) (where eta is the linear predictor from the dispersion model)". Does this indicate that these estimates of the Dispersion model appear on the log scale, and to get phi, they must be back-transformed?

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