   
   Actually, it´s interesting to know that it's a natural property of non-mixed 
models, as I was taught about preventing it with non-mixed glmms (using glm 
function) and when I started using lmer I just assumed I had to test for it as 
well.

   Thank you very much for your answers.

   Iker





________________________________
De: Paul Johnson <pauljohn32@gmail.com>
Para: r-sig-mixed-models@r-project.org
Enviado: jue,23 junio, 2011 20:00
Asunto: Re: [R-sig-ME] Is it worth testing for overdispersion?


ote:
>
>
>    Dear list:
>
>    I read some time ago in one of the posts that the option of implementing 
>quasi- families in lmer had been removed. Is that right?

You are confusing 2 things.  Overdispersion can occur, it may be a problem.

But, we believe the "quasi" sorts of models are just wrong, and if you
are going to treat over dispersion, you need to treat it properly,
either by changing to a negative binomial model or by introducing a
"real" mixed effect, not a quasi approximation of a mixed effect.
>

Overdispersion would naturally be a property of a non-mixed model,and
you can test for it in many ways. Could I suggest to you Simon
Jackman's package, "pscl", which includes some nice tools for that.

PJ

-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas

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