Common Agency and Computational Complexity: Theory and Experimental Evidence

In a common agency game, several principals try to influence the behavior of an agent. Common agency games typically have multiple equilibria. One class of equilibria, called truthful, has been identified by Bernheim and Whinston and has found widespread use in the political economy literature. In this paper we identify another class of equilibria, which we call natural. In a natural equilibrium, each principal offers a strictly positive contribution on at most one alternative. We show that a natural equilibrium always exists and that its computational complexity is much smaller than that of a truthful equilibrium. To compare the predictive power of the two concepts, we run an experiment on a common agency game for which the two equilibria predict a different equilibrium alternative. The results strongly reject the truthful equilibrium. The alternative predicted by the natural equilibrium is chosen in 65% of the matches, while the one predicted by the truthful equilibrium is chosen in less than 5% of the matches.lobbying;experimental economics;common agency;truthful equilibrium;natural equilibrium;computational complexity

A Theory of Sequential Reciprocity

Many experimental studies indicate that people are motivated by reciprocity. Rabin (1993) develops techniques for incorporating such concerns into game theory and economics. His model, however, does not fare well when applied to situations with an interesting dynamic structure (like many experimental games), because it is developed for normal form games in which information about the sequential structure of a strategic situation is suppressed. In this paper we develop a theory of reciprocity for extensive games in which the sequential structure of a strategic situation is made explicit. We propose a new solution concept— sequential reciprocity equilibrium—which is applicable to extensive games, and we prove a general equilibrium existence result. The model is applied in several examples, including some well known experimental games like the Ultimatum game and the Sequential Prisoners’ Dilemma.Reciprocity;extensive games

Does Learning Lead to Coordination on Market Clearing Institutions?

This paper analyzes the question whether traders learn to coordinate on a trading institution that guarantees market clearing, or whether other market institutions can survive in the long run. While we find that the market clearing institution is indeed always stable under a general class of learning dynamics, it turns out that also other, non-market clearing institutions are stable. Hence, in the long run traders may fail to coordinate exclusively on market clearing institutions.industrial organization ;

Does Learning Lead to Coordination in Market Clearing Institutions?

This paper analyzes the question of whether traders learn to coordinate on a trading institution that guarantees market clearing, or whether other market institutions can survive in the long run. While we find that the market clearing institution is indeed always stable under a general class of learning dynamics, it turns out that also other, non-market clearing institutions are stable. Hence, in the long run traders may fail to coordinate exclusively in market clearing institutions.

Your Morals Are Your Moods

We test the effect of players' moods on their behavior in a gift-exchange game. In the first stage of the game, player 1 chooses a transfer to player 2. In the second stage, player 2 chooses an effort level. Higher effort is more costly for player 2, but it increases player 1's payoff. We say that player 2 reciprocates if effort is increasing in the transfer received. Player 2 is generous if an effort is incurred even when no transfer is received. Subjects play this game in two different moods. To induce a `bad mood', subjects in the role of player 2 watched a sad movie before playing the game; to induce a `good mood', they watched a funny movie. Mood induction was effective: subjects who saw the funny movie reported a significantly better mood than those who saw the sad movie. These two moods lead to significant differences in player 2's behavior. We find that a bad mood implies more reciprocity while a good mood implies more generosity. Since high transfers are relatively more common, player 1 makes more money when second movers are in a bad mood.

The Endogenous Evolution of Market Institutions: An Experimental Investigation

We study an experimental market in which the structure of the information flows is endogenized. When making an offer, traders choose not only the price at which they are prepared to trade, but also the subset of traders they want to inform about the offer. This design allows for two extreme institutions as special cases. If traders always inform every other trader about each offer, the resulting institution is equivalent to a double auction. If, on the other hand, traders always inform only one other trader about each offer, the resulting institution is equivalent to a decentralized bargaining market. The institution that actually evolved in the experiments, however, was in between the two extreme cases. Subjects typically informed all traders of the other market side, but none of their own side. This endogenously evolving institution, however, turned out to have the same properties as the double auction.market institution;information structure;efficiency

Learning to Like What You Have - Explaining the Endowment Effect

The endowment effect describes the fact that people demand much more to give up an object than they are willing to spend to acquire it. The existence of this effect has been documented in numerous experiments. We attempt to explain this effect by showing that evolution favors individuals whose preferences embody an endowment effect. The reason is that an endowment effect improves one's bargaining position in bilateral trades. We show that for a general class of evolutionary processes strictly positive endowment effects will survive in the long run.endowment effect, evolution, bargaining