[R-sig-ME] Shape parameter for Gamma glmer?

Miranda Fix m|r@nd@@||x @end|ng |rom gm@||@com
Thu Apr 28 23:32:12 CEST 2022


My understanding is that one can obtain the Gamma shape parameter from a
glmer object, let's say "mod", by 1/sigma(mod)^2. In other words, 1 over
the dispersion. However, for a glm the dispersion is only a crude estimate
and there is a gamma.shape function in the MASS package to provide a better
estimate of the shape parameter. So my question is twofold:

1) Is sigma(mod)^2 a good estimate of the dispersion in the glmer case?
(i.e., is 1/sigma(mod)^2 a good estimate of the shape?)

2) If not, is there an equivalent of MASS::gamma.shape for a glmer object
instead of a glm object?

Thanks so much for your help!

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