In a duopoly where one firm has the idea for a non-patentable innovation, the expected profits from the innovation will not be a monotonic function of the cost of innovating. Furthermore, a costly innovation may be undertaken, where an inexpensive one would not have been, all other things being equal.

It is common for a majority of people to rank themselves as better than average on simple tasks and worse than average on difficult tasks. The literature takes for granted that this apparent misconfidence is problematic. We argue, however, that this behavior is consistent with purely rational Bayesian updaters. In fact, better-than-average data alone cannot be used to show overconfidence; we indicate which type of data can be used. Our theory is consistent with empirical patterns found in the literature.

We study subgame perfect equilibria of finitely repeated games. We prove a limit "folk theorem" for these games. Under weak conditions, any feasible and individually rational payoff vector of the one-shot game can be approximated by the average payoff in a perfect equilibrium of a repeated game with a sufficiently long horizon.

We study a dynamic model of duopoly in which firms choose both prices and quantities. If quantity (capacity) choices are relatively inflexible, firms generally carry excess (idle) capacity in equilibrium. Because of this enforcement cost, firms are unable to achieve monopoly levels. This contrasts with models in which which firms compete in either prices or quantities alone. On the other hand, if capacities are flexible firms may be able to sustain monopoly behaviour.

Perfect equilibria of finitely repeated games may be vulnerable to the possibility of renegotiation among players. We study the limiting properties of the set of payoffs from equilibria that are immune to renegotiation. Our main result is that the limit of the set of payoffs from renegotiation proof equilibria is either a singleton or a connected subset of the Pareto efficient frontier. A simple sufficient condition for the latter to occur is also provided.