Is it worth testing for overdispersion?
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