[R-sig-ME] Is it worth testing for overdispersion?

[Paul Johnson]

On Tue, Jun 21, 2011 at 6:53 AM, Iker Vaquero Alba <karraspito at yahoo.es> wrote:
>
>
>    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