R help - Oct 2008 - Overdispersion in the lmer models

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]]

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]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>