[R-sig-ME] How to analyse data with two replicates per group

[Simon POTIER]

Dear all,

Thanks in advance for your help.
I will try to be precise, do not hesitate to tell me if you need more
details.

I have a dataset measuring some features of raptors eyes (let says here eye
size for exemple). I have measured both eyes (left and right eyes) of 47
individuals.
If I want to compare eye size with age and sex, what type of analysis
should I use:

1) Should I analyse both eye separately (which can be interesting in term
of vision)?
2) Can/should I analyse both eye together including Individual as a random
effect? In other terms, I was wondering whether including individuals as
random effect (with only two levels for each individual (left and right
eye)) is possible?

One more question, I want to compare the AIC of my models, but I get this
error message:
Warning message:
In AIC.default(mm.edge, mm.edge2, mm.edge3) :
  models are not all fitted to the same number of observations

I understand that the problem come from the fact that I have some NA in
some fixed effect. How can I deal with this please because it is not
possible to compare AIC?

Best regards,

Simon Potier

-- 
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Simon Potier
Department of Biology
Lund University
Sölvegatan 35
S-22362 Lund
Sweden
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phone +336 11 31 67 16
sim.potier using gmail.com
https://www.simonpotier.fr
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