[R] Overdispersion in count data

From: Wade Wall <wade.wall_at_gmail.com>
Date: Wed, 02 Apr 2008 12:03:37 -0400

Hi all,

I have count data (number of flowering individuals plus total number of individuals) across 24 sites and 3 treatments (time since last burn). Following recommendations in the R Book, I used a glm with the model y~ burn, with y being two columns (flowering, not flowering) and burn the time (category) since burn. However, the residual deviance is roughly 10 times the number of degrees of freedom, and using the quasibinomial distribution doesn't change this. Any suggestions as to why the quasibinomial distribution doesn't change the residual deviance and how I should proceed. I know that this level of residual deviance is unacceptable, but not sure is transformations are in order.

Needless to say that I am at the outer limits of my statistical knowledge.

Thanks for any help,

Wade Wall

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