I am trying to combine two AIC scores from different parts of a single data set. I have two sigmoidal models that each predict about half of the data (imagine two sigmoidal curves attached end to end), each with a different AIC. I am interested in finding the combined AIC of both curves to represent the single, total AIC of the combined models. I have been told that this is possible, but I don't know how. Any suggestions are much appreciated!