
   Dear list:

   I am fitting a model in lmer, which a colleague has told me could be incurring collinearity. I have been gathering all the information I could about the subject, but I don't think I still have things very clear, so maybe you can help me.

   First of all, I have red in some place that depending on your purpose, maybe dealing with collinearity is not so important:

   "one more
thing,if your purpose of modeling is prediction but not
interpretation,collinearity does not matter much."

   I´m not sure I've properly understood this. Anyone would be so kind as clarify it a bit more and tell me wether that is right?

   Further to that, as my model is fitted with lmer, I cannot use "vif" function from package car. But I have found another function called "vif.mer". Any of you knows it, and does it work as "vif" for lm objects?

   My model includes several colour measurements from some male guppies as independent variables. I would expect them to be independent as their production comes from different metabolic routes: one of the variables corresponds to carotenoid-related pigments, another one to melanin-related and another one to structural colours. The problem could come from the fact that I've also included the area occupied by colour in relation to the total body area (a proportion). As the individual colour areas are absolute values and the total colouration area is a proportion of the total body area, I supposed it should not be a problem. I also included body length and a factor called "predator", with 4 levels, and several first order interactions between the variables The model is as follows:

   guppymodel1<-lmer(boldscore~blength+proptarea+carot+black+struct+predator+blength:proptarea+blength:carot+blength:black+blength:struct+predator:proptarea+predator:carot+predator:black+predator:struct+proptarea:carot+proptarea:black+proptarea:struct+carot:black+carot:struct+black:struct+(1|pair)+(1|timeday)+(1|torder))

   Do you think it could be incurring collinearity, and is it necessary to deal with it?

   Thank you very much.

________________________________________

   Iker Vaquero-Alba
   Centre for Ecology and Conservation
   Daphne du Maurier Building
   University of Exeter, Cornwall Campus
   Treliever Road
   TR10 9EZ Penryn
   U.K.

   http://biosciences.exeter.ac.uk/cec/staff/postgradresearch/ikervaquero-alba/



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