Role of the Minimal State Variable Criterion
This paper concerns the minimal-state-variable (MSV) criterion for selection among solutions in rational expectations (RE) models that feature a multiplicity of paths that satisfy all of the model's conditions. It compares the MSV criterion with others that have been proposed, including the widely used saddle-path (or dynamic stability) criterion. It is emphasized that the MSV criterion can be viewed as a classification scheme that delineates the unique solution that is free of bubble or sunspot components. This scheme is of scientific value as it (a) yields a single solution upon which a researcher can focus attention if desired and (b) provides the basis for a substantive hypothesis that actual market outcomes are generally of a bubble-free nature. In the process of demonstrating uniqueness of the MSV solution for a broad class of linear models, the paper exposits a convenient and practical computational procedure. Also, several applications to current issues regarding monetary policy are outlined.