Spillovers and innovative activities

This paper reports a search for general tendencies among models that look at spillovers in innovative activities. A number of inferences are detailed that appeared in a wide class of settings, including stochastic racing models, (static) stochastic models, dynamic and static commitment models, and strategic investment models. They include: - the role of a critical spillover level that drives the comparison between symmetric cooperative and non-cooperative efforts; - the disincentive effect of symmetric spillovers for strategic investments and the positive effect of such spillovers for investment commitments and cooperative efforts; - the fact that innovative output in many cases is highest when appropriation is neither perfect nor free, although circumstances also emerge where any lack of appropriation will discourage innovative efforts.