[R] Overdispersion in the lmer models

David Winsemius dwinsemius at comcast.net
Mon Oct 13 21:30:50 CEST 2008

Dear Eva;

I shouldn't have sent my unhelpful reply to the entire list, since it  
is now glaringly obvious that I did not carefully read your original  
question. You are outside my experience, since I have not used lme4,   
but I wonder if questions about over-dispersion shouldn't be handled  
by examining grouped residuals? According to the documentation,  "mer"  
models have a resid method, although the help page it links to appears  
to be "under construction".

David Winsemius
Heritage Laboratories

On Oct 13, 2008, at 4:46 AM, Fucikova, Eva wrote:

> Dear David,
> Thank you for such a fast answer. Unortunatelly, your suggestion does
> not work for lmer for some reason. I can probably try to run the model
> without random effect to find out the overdispersion in the glm.
> Anyway, thank you very much.
> Yours sincerely,
> Eva
> -----Original Message-----
> From: David Winsemius [mailto:dwinsemius at comcast.net]
> Sent: maandag 13 oktober 2008 3:42
> To: Fucikova, Eva
> Cc: r-help at r-project.org
> Subject: Re: [R] Overdispersion in the lmer models
> Have you considered  using glm() with  family = "quasipoisson" or  
> family
> = quasibinomial ? I know from experience that the quasipoisson choice
> reports an index of dispersion.
> ?family
> --
> David Winsemius
> On Oct 12, 2008, at 4:55 AM, Fucikova, Eva wrote:
>> Dear All,
>> I am working with linear mixed-effects models using the lme4 package
>> in R. I created a model using the lmer function including some main
>> effects, a three-way interaction and a random effect.
>> Because I work with a binomial and poisson distribution, I want to
>> know whether there is overdispersion in my data or not. Does anybody
>> know how I can retrieve this information from R?
>> Thank you in advance,
>> Eva Fucikova
>> 	[[alternative HTML version deleted]]
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