Ana B. Ania

An Evolutionary Model of Bertrand Oligopoly

We analyze the long-run outcome of markets in which boundedly rational firms with a decreasingreturns to scale technology compete in prices. The behavior of these firms is based on limitation ofsuccess and experimentation. In this framework, we introduce a new approach to model boundedlyrational behavior, based on the idea of behavioral principles, i.e. formal descriptions. Even with thesimplest ones, the result is that the prices announced are a strict refinement of the set of Nashequilibria. With more sophisticated behavioral principles, the long-run outcome corresponds to theconcept of central prices (wich are also Nash equilibria) introduced here. This is a robust andclear-cut prediction wich, under quadratic costs and arbitrary demand, essentially coincides with theWalrasian equilibrium.

An evolutionary analysis of insurance markets with adverse selection

Since the seminal work by Rothschild and Stiglitz on competitive insurance markets under adverse selection the problem of non-existence of equilibrium hat puzzled many economists. In this paper we approach this problem from an evolutionary point of view. In a dynamic model insurance companies remove lossmaking contracts from the market and copy profit making ones. Occasionally, they also experiment, adding new contracts or removing current ones arbitrarily. We show that the Rothschild-Stiglitz outcome arises in the long run if it cinstitutes an equilibrium in the static framework, but also if it is not an equilibrium, provides that firms only experiment with contracts in the vicinity of their current portfolio.

Local equilibria in economic games

We study solution concepts for economic games that are resistant to local deviations. Strategy spaces are l subsets of R and local deviations are small in the Euclidean metric. We definelocal Nash equilibrium and local evolutionarily stable strategy, and present applications to Walrasian outcomes in Cournot games and separating outcomes in screening models.