[R-sig-eco] GLM mixed model with quasibinomial family

Javier Martinez javi.martinez.lopez at gmail.com
Thu Jul 29 18:07:44 CEST 2010

Thanks to all of you! I did know the e-mail by Bates, which is out of
my understanding, but I did not know the wiki on mixed models and the
manuscript by Bolker! My data are based on 2 temporal samples from 8
different sites. I use mixed models because I want to avoid
pseudo-replication including the grouping factor into my model and
thus looking for the trends within each group and not looking at the
data as if they were independent. The question is, can I really use a
mixed model if I only have two cases per group? At the end there are
16 cases in the regression plot but I am not sure if such a grouped
analysis is right!

Thank you again for your help!


On Wed, Jul 28, 2010 at 6:44 PM, Javier Martinez
<javi.martinez.lopez at gmail.com> wrote:
> Dear R-users,
> I am using the 'lmer' function from package 'lme4', looking for a
> regression model which takes into account the grouped nature of my
> data. I am using frequencies as the dependent variable and percentages
> as the independent one. After some reading I think I should use the
> 'quasibinomial' family because there is 'overdispersion' in my data
> set (greater residual deviance than residual degrees of freedom). So,
> I test this regression model but I do not get a significance p-value
> for the regression! I have to test many different regressions with
> different data, so how can I assess the significance of each of of
> them?
> Thank you very much for your help!
> Javier

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