I'm using SPSS to try and find a mixed model that adequate explains the data that I have. Two of the explanatory variables are closely related ('Sample group' and 'individual'), as an individual is only ever part of one sample group, so I've been nesting them if they are in the same model.
I've been using the models AIC score to rank the models in order of explanatory power. Some of the models use the nested variables, and some of the models only use either 'Sample group' or 'individual'.
My question is: Is it valid to use the AIC to compare between models that use nested variables and those that don't?
To clarify by nested variables, I mean that some of the potential variables used in a model are: 1) sample site(individual) 2) sample site 3) individual