Mixed Nash equilibria are a cornerstone of game theory, but their empirical relevance has always been controversial. We study in the laboratory two games whose unique NE is in completely mixed strategies; other treatments include the matching protocol (pairwise random vs population...

A preference for negative reciprocity is an important part of the human emotional repertoire. We model its role in sustaining cooperative behavior but highlight an intrinsic free-rider problem: the fitness benefits of negative reciprocity are dispersed throughout the entire group, but the...

We discuss how small group interactions overcome evolutionary problems that might otherwise erode vengefulness as a preference trait. The basic viability problem is that the fitness benefits of vengeance often do not cover its personal cost. Even when a sufficiently high level of vengefulness...

This paper analyzes seller characteristics and choices in approximately 1000 eBay auctions for a particular model of PDA. Seller characteristics include frequency of selling, reputation, and the qualities of the product sold. Seller choices include the length of the auction, information provided...

This paper analyzes seller choices and outcomes in approximately 700 recent Internet auctions on eBay. The 'Buy it Now' option that is available in these auctions allows the seller to supplement or replace the auction with a posted price offer. We use a structural model to control for the...

This paper develops a theory of revealed preferences over one.s own and others.monetary payoffs. We introduce .more altruistic than.(MAT), a partial ordering over preferences, and interpret it with known parametric models. We also introduce and illustrate .more generous than. (MGT), a partial...

A human subject laboratory experiment compares the real-time market performance of the two most popular auction formats for online ad space, Vickrey-Clarke-Groves (VCG) and Generalized Second Price (GSP). Theoretical predictions made in papers by Varian (2007) and Edelman, et al. (2007) seem to...

A complete set of transactions, more than 40 million within a 1.8 year span, allows us to track the evolution of the trader network and the goods network in an on-line trading community. The computer platform was designed to make barter exchange as attractive as possible; money was not part of...

Human players in our laboratory experiment received flow payoffs over 120 seconds each period from a standard Hawk-Dove bimatrix game played in continuous time. Play converged closely to the symmetric mixed Nash equilibrium under a one-population matching protocol. When the same players were...

We develop a financial market model focused on fund managers who continuously adjust their exposure to risk in response to the payoff gradient. The base model has a stable equilibrium with classic properties. However, bubbles and crashes occur in extended models incorporating an endogenous...