New Developments in Automatic General-to-Specific Modeling.

We consider the analytic basis for PcGets, an Ox Package implementing automatic generalto- specific (Gets) modelling for linear, dynamic, regression models. PcGets mimics the theory of reduction – whereby empirical models arise – by commencing from a general congruent specification, which is then simplified to a minimal representation consistent with the desired selection criteria and the data evidence. We discuss the properties of PcGets, since results to date suggest that model selection can be relatively non-distortionary, even when the mechanism is unknown, and contrast Gets with possible alternatives