[R-sig-ME] degrees of freedom in Gamma GLMMs

Klaus, J. (Jana) j.klaus at donders.ru.nl
Mon Feb 19 10:25:25 CET 2018

Hi all,


I have fitted a GLMM with a Gamma distribution with crossed random effects in lme4 for reaction times, like this:


model = glmer(RT~Factor1*Factor2+ (1+Factor1+Factor2|subj) + (1+Factor1|item), data=xdat, family = Gamma(link = "identity"), control=glmerControl(optimizer = "bobyqa"))


The editor now insists on reporting degrees of freedom. From what I have found online, this is not trivial, and potentially not at all possible with the design. I fit the same model with glmmPQL but I cannot reproduce the results, presumably because the random effects are treated as nested rather than crossed there. Also, as far as I can tell, all other workarounds to compute dfs do not apply to this specific design. Nevertheless, I’m afraid I might be overlooking something essential already implemented in lme4 (or any other package for that matter). If this is not the case, could you point me towards any work that explains *why* it can’t be done for GLMMs? Any help is greatly appreciated!




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