Modelling Imperfectly Appropriable R&D via Spillovers

We provide an extensive comparison of the R&D models of d'Aspremont-Jacquemin (1988) and Kamien-Muller-Zang (1992), exposing full or partial conflict in key conclusions and policy prescriptions. Using three separate formal and/or intuitive criteria, we argue that the first model is invalid for large spillover values. This conclusion is corroborated by an additional argument leading to equivalence between the two R&D processes, but not to agreement on some key conclusions. Hence, the models emerge as fundamentally different, although a unilateral shift in the cost function of the first leads to agreement in all equilibrium outcomes.