Hi all,

I am attempting to analyze my field data from last year in SPSS. In a nutshell, I am running a generalized linear mixed model, and I have one fixed effect and one random effect. The fixed effect is continuous, while the random effect is categorical. I notice in SPSS it gives you the option to include or not include intercepts for both fixed and random effects. Should I be including the intercepts for both effects, only the fixed effect, or only the random effect? I would love to understand more about intercepts and how to determine when it is appropriate to include them in these types of models.

*P.S.* The model using intercepts for both fixed and random effects has a higher AIC value than the model using an intercept only for the fixed effect, so I am inclined to use the latter model.