Before you go down this road, consider whether you really want to find a "best" model.  There are tons of posts in this forum that point out the problems with any of the selection methods and criteria.  Since model building is an art, you should consider the physical/biological/psychological processes involved and use that prior knowledge to form hypotheses about the relationship you are testing. Should you merely want the best predictor, use all the variables and their interactions and do something like a classification and regression tree approach.  Pure regression "ought" to have something to do with an assumed causality, otherwise you may as well include number of sunspots observed as a predictor.   SteveDenham ... View more