I consider a first model where the 6 observables (concentrations of metabolites) are fitted on the data set (the experimental measure of these 6 concentrations). I also have a second model, that is a subset of the first one and models only 4 observables. This second model is fitted on only a part (4 out of 6 concentrations) of the data set used for the first model.
I cannot use the AIC to compare the two models because they are not fitted on exactly the same data. Is these an extension of the AIC or another information criterion that could help me in my case of "nested" models and "nested" data? (If you have a reference, would be great!)