Evolution of networks—an experimental analysis

It is the main aim of our paper to study network formation in experimental setups in discrete and continuous time. Our design is inspired by the theoretical model on network formation by Bala and Goyal (Econometrica, 68(5): 1181–1229, 2000) as well as the experiments by Callander and Plott (J. Public Econ., 89: 1469–1495, 2005) and Falk and Kosfeld (IEW Working Paper, University of Zürich, Zürich, Switzerland, No. 146, 2003). In particular, we analyze the role of star-shaped networks which are strict Nash-equilibria of the corresponding network formation game. Our experimental results show that strict Nash networks prove to be a good indicator for predicting network formation, particularly in continuous time. In explaining our results, it turns out that, among others, the complexity in coordinating on stars, the inequity aversion against unequal payoff distribution in the network, and the groups’ degrees of activity are the most important determinants for the formation of strict Nash networks.      

A network experiment in continuous time: The influence of link costs

In recent work on non-cooperative network formation star-shaped networks play an important role. In a particular theoretical model of Bala and Goyal (2000) center-sponsored stars are the only strict Nash networks. In testing this theoretical model, Falk and Kosfeld (2003) do not find experimental evidence that players select the center-sponsored star. Based on a slight modification of Bala and Goyal’s model, we design a network formation experiment in which, depending on link costs, periphery-sponsored stars and the empty network are the only strict Nash networks. We observe that almost all groups not only reach a strict Nash network once but also switch the center player in periphery-sponsored stars several times. The main innovation in our experiment is to use a continuous time framework which we believe to be a more realistic setting to study behavior in network formation situations and which makes coordination on stars much easier than simultaneous strategy adaptation in discrete time. Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10683-006-9125-1. JEL Classification C72 · C92 · D81     

BUYING VERSUS HIRING—AN INDIRECT EVOLUTIONARY APPROACH

On a symmetric homogeneous oligopoly market with stochastic demand, firms can either hire employees or buy their labor input on a competitive labor market. Whereas the wage of hired labor does not depend on the realization of stochastic demand, the price of ‘bought’ labor reacts positively to product demand. We derive the equilibrium price vector to define an evolutionary process, assuming that the number of hiring firms increases when they earn more than buying firms. We then derive and discuss the stationary distribution of this stochastic adaptation process.     

Conventions,local interaction,and automata networks

This paper deals with the evolution of conventions in a finite population of boundedly rational players. We apply methods from the theory of automata networks to analyze the effects of different interaction structures. It is shown that the size of the reference group for each player has an important impact on the evolutionary stability of a particular convention, and that the interaction structure crucially determines the distribution of conventions in the population.     

DUOPOLISTIC HIRING AND SALES COMPETITION—A THEORETICAL AND EXPERIMENTAL ANALYSIS

Two firms compete in selling as well as hiring, where sales levels depend on the hired workforce. There are two types of workers, mobile and immobile, differing in effort costs, and two workers of each type. The principals offer contracts to all workers, who then select an employer. Finally, the workers determine production levels and profits. Our experimental results show: vanishing cost differences between mobile and immobile workers induce monopolistic hiring but low profits. In contrast, large cost differences result in higher profits and allow for various hiring constellations such as one firm hiring only low‐cost workers.     

Zur Wirkung regulatorischer Preiseingriffe auf dem Tankstellenmarkt

Das Bundeskartellamt hat die M?rkte für Benzin und Diesel in Deutschland untersucht und ein oligopolistisches Umfeld diagnostiziert, das zu erh?hten Preisen führt. Der Nutzen eines regulatorischen Eingriffs nach dem Vorbild des „?sterreichischen Modells“ wird jedoch sowohl vom Amt als auch von der Fach?ffentlichkeit in Frage gestellt. Diese preisregulatorische Ma?nahme wird hier spieltheoretisch und experimentell analysiert.     

Reciprocity—an indirect evolutionary analysis

This paper investigates agents who face a stylized pecuniary ‘game of life’ comprising the ultimatum game and the dictator game. Utility may but need not be attached to equity and reciprocity, as formalized by Falk and Fischbacher (Games Econom Behav, 54(2): 293–315, 2006) but, critically, this social component of preferences cannot be conditioned on whether an ultimatum or a dictator game is played. Evolutionary fitness of agents is determined solely by material success. Under these conditions, a strong preference for reciprocity, but little interest in equity as such evolves. Possible exogenous constraints that link reciprocity and equity concerns imply long-run levels of both which depend on the relative frequency of ultimatum vs. dictator interaction in agents’ multi-game environment. Financial support from the German Academic Exchange Service (DAAD) is gratefully acknowledged.     

The power of ESS: An experimental study

Abstract. Our experimental design mimics a traditional evolutionary game framework where players are matched pairwise to play a symmetric 33 bimatrix game that has two Nash equilibria. One equilibrium is an evolutionary stable state, or ESS; the other is an equilibrium in dominated strategies. Our primary experimental result is the observation that the ESS becomes extremely attractive when subjects have minimal information about the payoff functions, although the dominated equilibrium assures the highest equilibrium payoff. The attractiveness of the ESS is only moderate when players are completely informed about the 33 payoff matrix. Correspondence to: S.K. Berninghaus     

Conventions and Local Interaction Structures: Experimental Evidence

We present a series of experimental coordination games with a payoff-dominant and a risk-dominant Nash equilibrium. We examine how much local interaction structures affect players' strategy choices. Our three major observations are the following: First, local interaction with open neighborhoods along a circle leads to less coordination on the payoff-dominant equilibrium than interaction in closed neighborhoods. Second, when players are allocated around a circle, the neighborhood size has, in the long run, no effect on the players' strategy choices. Third, with the same neighborhood size, players allocated on a lattice tend less than players allocated around a circle to coordinate on the payoff-dominant equilibrium. This is true even though the players are given exactly the same instructions. Journal of Economic Literature Classification Numbers: C72, C92.