COOPERATION IN VISCOUS POPULATIONS - EXPERIMENTAL EVIDENCE

We experimentally investigate the effect of population viscosity (an increased probability to interact with others of one's type or group) on cooperation in a standard prisoner's dilemma environment. Subjects can repeatedly choose between two groups that differ in the defector gain in the associated prisoner's dilemma. Choosing into the group with the smaller defector-gain can signal one's willingness to cooperate. The degree of viscosity is varied across treatments. We find that viscosity produces an endogenous sorting of cooperators and defectors and persistently high rates ofcooperation. Higher viscosity leads to a sharp increase in overall cooperation rates and in addition positively affects the subjects' intrinsic willingness to cooperate.Experiments, Cooperation, Group Selection, Norms, Population

Solving the incomplete markets model with aggregate uncertainty using the Krusell-Smith algorithm

This paper studies the properties of the solution to the heterogeneous agents model in Den Haan, Judd and Juillard (2008). To solve for the individual policy rules, we use an Euler-equation method iterating on a grid of prespecified points. To compute the aggregate law of motion, we use the stochastic-simulation approach of Krusell and Smith (1998). We also compare the stochastic- and non-stochastic-simulation versions of the Krusell-Smith algorithm, and we find that the two versions are similar in terms of their speed and accuracy.

The Dynamics of Cooperation in Group Lending - A Microfinance Experiment

We investigate the dynamics of borrower behavior in a microfinance experiment in which subjects are jointly responsible for credit repayment. Although cooperation levels are generally high, moral hazard problems persist among borrowers. Moreover, the path dependency of decisions mitigates the insurance effect of joint liability. We compare two conversion mechanisms from joint to individual liability. First, an active choice of the joint liability contract does not systematically increase cooperation. Second, conversion based on repayment success tends to have a detrimental impact on cooperation among the remaining joint liability borrowers.microfinance, group lending, individual lending, social preferences

Strategic behavior in repeated voluntary contribution experiments

We conduct a repeated VCM (voluntary contribution mechanism) experiment using thestrategy method. We compare a partner and a stranger design and find that participantsin the partner treatment provide (i) higher initial contributions, (ii) higher contributionson average over all periods, and (iii) contributions that do not vary more strongly withpast contributions than participants in the stranger treatment. We conclude from ourevidence that strategic motives can account for a large share of the treatment differencestypically observed in this literature.public economics ;

Expectations and Forward Risk Premium in the Spanish Power Market

To analyse the forward risk premium in the Spanish electricity market, we adopt not only an ex post approach, but also an ex ante. We find that the sign of the ex post forward premium depends on the unexpected variation in demand and on the unexpected variation in the hydro-energy capacity, and that the ex ante forward premium varies with the expected demand in tight market conditions, showing that the participation of forward dealing agents in the Spanish market responds to risk considerations. Moreover, we find support for the implications derived from the Bessembinder & Lemmon (2002) equilibrium model.

Cooperation, Imitation and Correlated Matching

We study a setting where imitative players are matched into pairs to play a Prisoners' Dilemma game. A well know result in such setting is that under random matching cooperation vanishes for any interior initial condition. The novelty of this paper is that we add a certain correlation to the matching process: players that belong to a pair were both parties cooperate repeat partner next period whilst all other players are randomly matched into pairs. This intuitive correlation introduced in the matching process makes cooperation the unique outcome in the long run under some conditions. Furthermore, we show that no assortative equilibrium exits.Cooperation; Correlated Matching; Imitation; Prisoners' Dilemma

Cooperation through Imitation and Exclusion in Networks

We develop a simple model to study the coevolution of interaction structures and action choices in Prisoners’ Dilemma games. Agents are boundedly rational and choose both actions and interaction partners via payoff-based imitation. The dynamics of imitation and exclusion yields polymorphic outcomes under a wide range of parameters. Depending on the parameters of the model two scenarios can arise. Either there is “full separation” of defectors and cooperators, i.e. they are found in two different, disconnected components. Or there is “marginalization” of defectors, i.e. connected networks emerge with a center of cooperators and a periphery of defectors. Simulations confirm our analytical results and show that the share of cooperators increases with the speed at which the network evolves, increases with the radius of interaction and decreases with the radius of information of agents.Game Theory, Cooperation, Imitation Learning, Network Formation

The evolution of universal cooperation

Humans work together in groups to tackle shared problems and contribute to local club goods that benefit other group members. Whereas benefits from club goods remain group bound, groups are often nested in overarching collectives that face shared problems like pandemics or climate change. Such challenges require individuals to cooperate across group boundaries, raising the question how cooperation can transcend beyond confined groups. Here, we show how frequent intergroup interactions allow groups to transition from group-bound to universal cooperation. With frequent intergroup interactions, reciprocity of cooperative acts permeates group boundaries and enables the evolution of universal cooperation. As soon as intergroup interactions take place frequently, people start to selectively reward cooperation aimed at benefitting everyone, irrespective of their group membership. Simulations further show that it becomes more difficult to overcome group-bound cooperation when populations are fragmented into many small groups. Our findings reveal important prerequisites for the evolution of universal cooperation. + Figure

Natural groups and economic characteristics as driving forces of wage discrimination

We investigate whether the origin of an employee provides different motives for wage discrimination in gift-exchange experiments with students and migrant workers in China. In a lab and an internet experiment, subjects in the role of employers can condition their wages on the employees' home provinces. The resulting systematic differences in wages can be linked to natural groups and economic characteristics of the provinces. In-group favoritism increases wages for employees who share the same origin as the employer, while an increased probability of being matched with an employee with a different ethnicity reduces wages. Furthermore, wages in the laboratory increase with the actual wage level in the employees׳ home province. Nevertheless, employees' effort is not influenced by these variables; only the wage paid in the experiment influences effort

Triangulation of Qualitative and Quantitative Methods in Panel Peer Review Research

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