
Thanks for the reply.  Yes, ancestry is unrelated to social grouping as I've excluded all closely related animals.  Generally its simply an unrelated male and female breeder.  The groups are 1-4 individuals (not all individuals in each group are sampled of course).
However, I've realized I hadn't thought it through well enough.  While in some cases the independent variables are identical within group (they are based on environmental characteristics of annual home ranges) in other cases they are not.  Thus, I couldn't present the correlation matrices by group unless I averaged the variables across individuals within the same group.  This seems flawed because the mean values would not be the actual data used for regression.  Therefore, I've decided to simply present the correlation matrix by individuals, knowing that these may overstate the correlation in terms of its effect on the analysis, given that I've accounted for correlation within group with the random variable.
Sorry for the confusion.  I would still be interested in any thoughts on this, although I think I've got a plan.....
John

> Date: Sat, 11 Aug 2012 08:28:34 +1000
> From: David.Duffy@qimr.edu.au
> To: smilodon2000@hotmail.com
> CC: r-sig-mixed-models@r-project.org
> Subject: Re: [R-sig-ME] correlations between fixed effects: groups or individuals for mixed models?
> 
> On Fri, 10 Aug 2012, john benson wrote:
> 
> > I've been using GAMMs and GLMMs to investigate genetic ancestry in 
> > relation to environmental heterogeneity.  My data come from individuals 
> > (n = 85) that live in social groups (n = 44) across my study area. 
> > Thus, I have included social group as a random effect and investigated 
> > the influence of several environmental fixed effects. My question: Given 
> > that the random effect of social group should account for 
> > non-independence between individuals within groups, it seems like I 
> > should only be concerned with correlations between independent variables 
> > across social groups (rather than across individuals).  Is it the 
> > convention with mixed models such as mine to report a correlation matrix 
> > between groups, or do folks generally report a correlation matrix 
> > between individuals as one would normally do with a GLM or GAM?  I 
> > suppose I could report both, but it seems like the correlations between 
> > individuals wouldn't be relevant given the inclusion of the random 
> > effect.
> 
> Two members per group? Or are they overlapping?  And ancestry is unrelated 
> to social grouping?
> 
> -- 
> | David Duffy (MBBS PhD)                                         ,-_|\
> | email: davidD@qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
> | Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
> | 300 Herston Rd, Brisbane, Queensland 4029, Australia  GPG 4D0B994A v
 		 	   		  
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