[R-sig-ME] Function to get residuals & fitted values from Poisson GLMM with OLRE
paul.johnson at glasgow.ac.uk
Wed Jul 27 12:29:45 CEST 2016
I’ve written a function which some might find useful. It outputs “corrected” Pearson residuals from a glmer fit of the form
fit <- glmer(y ~ . + (1 | obs), family = “poisson”)
where "(1 | obs)” fits an observation level random effect (OLRE), i.e. length(obs) == length(y).*
The function is called residfitted.olre and can be found here:
The default behaviour of residuals(fit) and fitted(fit) is to treat the OLRE as part of the fitted values, but for most practical purposes I want the OLRE to be in the residuals and not in the fitted values. In particular, if I’m using a residuals-vs-fitted-values plot to assess the fit, the default residuals and fitted functions used by plot(fit) will generally produce nasty-looking plots showing a trend and severe heteroscedasticity even from well fitting models. The “corrected” residuals fix this problem.
There’s also example code below the function showing how this it allows interpretable residuals-vs-fitted plots to be produced from a Poisson GLMM with an OLRE (aka a Poisson-lognormal GLMM).
The same problem affects a binomial GLMM with an OLRE, but I haven’t (yet) made the function work for binomial GLMMs for the reason covered in this post:
(basically I don’t know what the variance function is for a mixture of binomial + logit-normal — anyone know?).
Hope someone finds it useful,
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