Recently, there has been a Renaissance for multi-level selection models to explain the persistence of unselfish behavior in social dilemmas, in which assortative/correlated matching plays an important role. In the current study of a multi-round prisoners’ dilemma experiment, we introduce two correlated matching procedures that match subjects with similar action histories together. We discover significant treatment effects, compared to the control procedure of random matching. Particularly with the weighted history matching procedure we find bifurcations regarding group outcomes. Some groups converge to the all-defection equilibrium even more pronouncedly than the control groups do, while other groups generate much higher rate of cooperation, which is also associated with higher relative reward for a typical cooperative action. All in all, the data show that cooperation does have a much better chance to persist in a correlated/assortative-matching environment, as predicted in the literature.

We investigate the effects of centrality on cooperation in groups. Players with centrality keep a group together by having a pivotal position in a network. In some of our experimental treatments, players can vote to exclude others and prevent them from further participation in the group. We find that, in the presence of exclusion, central players contribute significantly less than others, and that this is tolerated by those others. Because of this tolerance, groups with centrality manage to maintain high levels of cooperation.

We develop a model that relates self-control to cooperation patterns in social dilemmas, and we test the model in a laboratory public goods experiment. As predicted, we find a robust association between stronger self-control and higher levels of cooperation, and the association is at its strongest when the decision maker’s risk aversion is low and the cooperation levels of others high. We interpret the pattern as evidence for the notion that individuals may experience an impulse to act in self-interest—and that cooperative behavior benefits from self-control. Free-riders differ from other contributor types only in their tendency not to have identified a self-control conflict in the first place.

We explore if fairness and inequality motivations affect cooperation in indefinitely repeated games. Each round, we randomly divided experimental participants into donor–recipient pairs. Donors could make a gift to recipients, and ex-ante earnings are highest when all donors give. Roles were randomly reassigned every period, which induced inequality in ex-post earnings. Theoretically, income-maximizing players do not have to condition on this inequality because it is payoff-irrelevant. Empirically, payoff-irrelevant inequality affected participants’ ability to coordinate on efficient play: donors conditioned gifts on their own past roles and, with inequalities made visible, discriminated against those who were better off.

This study investigates the mechanisms driving the effectiveness of free-form communication in promoting cooperation within a sequential social dilemma game. We hypothesize that the self-constructing nature of free-form communication enhances the sincerity of messages and increases the disutility of dishonoring promises. Our experimental results demonstrate that free-form messages outperform both restricted promises and treatments where subjects select and use previously constructed free-form messages. Interestingly, we find that selected free-form messages and restricted promises achieve similar levels of cooperation. We observe that free-form messages with higher sincerity increase the likelihood of high-price and high-quality choices, thereby promoting cooperation. These messages frequently include promises and honesty, while threats do not promote cooperation. Our findings emphasize the crucial role of the self-constructed nature of free-form messages in promoting cooperation, exceeding the impact of message content compared to restricted communication protocols.

We propose a novel experimental method that disentangles strategically- and non-strategically-motivated behavior. We apply it to an indefinitely-repeated prisoner's dilemma game to observe simultaneously how the same individual behaves in situations with future interaction and in situations with no future interaction, while controlling for expectations. This method allows us to determine the extent to which strategically-cooperating individuals are responsible for the observed pattern of cooperation in experiments with repeated interaction, including the so-called endgame effect. Our results indicate that the most common motive for cooperation in repeated games is strategic.

Previous research has suggested that communication and especially promises increase cooperation in laboratory experiments. This has been taken as evidence for internal motivations such as guilt aversion or preference for promise keeping. The goal of this paper was to examine messages under a double-blind payoff procedure to test the alternative explanation that promise keeping is due to external influence and reputational concerns. Employing a 2 × 2 design, we find no evidence that communication increases the overall level of cooperation in our experiments with double-blind payoff procedures. However, we also find no evidence that communication impacts cooperation in our experiments with single-blind payoff procedures. Further, the payoff procedure does not appear to impact aggregate cooperation.

Some peer punishment technologies may bias experimental results in unwanted ways. A critical parameter to consider in the design is the “fine-to-fee” ratio, which measures the income reduction for the targeted subject relative to the cost for the subject who requested the punishment. We show that a punishment technology commonly used in experiments embeds a variable fine-to-fee ratio and show that it could confound the empirical findings about why, whom, and how much subjects punish.

Ostracism is practiced by virtually all societies around the world as a means of enforcing cooperation. In this paper, we use a public goods experiment to study whether groups choose to implement an institution that allows for the exclusion of members. We distinguish between a costless exclusion institution and a costly exclusion institution that, if chosen, reduces the endowment of all players. We also provide a comparison with an exclusion institution that is exogenously imposed upon groups. A significant share of the experimental groups choose the exclusion institution, even when it comes at a cost, and the support for the institution increases over time. Average contributions to the public good are significantly higher when the exclusion option is available, not only because low contributors are excluded but also because high contributors sustain a higher cooperation level under the exclusion institution. Subjects who vote in favor of the exclusion institution contribute more than those who vote against it, but only when the institution is implemented. These results are largely inconsistent with standard economic theory but can be better explained by assuming heterogeneous groups in which some players have selfish and others have social preferences.

We experimentally study ways in which social preferences affect individual and group performance under indefinitely repeated relative incentives. We also identify the mediating role that communication and leadership play in generating these effects. We find other-regarding individuals tend to depress efforts by 15% on average. However, selfish individuals are nearly three times more likely to lead players to coordinate on minimal efforts when communication is possible. Hence, the other-regarding composition of a group has complex consequences for organizational performance.

This paper reports the results of the Ultimatum Game (UG), Dictator Game (DG) and Public Goods Game (PGG) played among the Tsimane, a group of forager-horticulturalists living in the Bolivian Amazon. Game results differ significantly from those commonly reported among modern, westernized populations. Without a long history of anonymous interactions, it is highly suspect whether the Tsimane or other traditional populations play economic games under assumptions of anonymity and one-shot exposure. Employing a behavioral ecology framework, I test predictions that differential market exposure, costs of giving, and experience with cooperation can help explain much of the variance in game outcomes. While these factors sometimes act as important predictors of game behavior, the most significant predictor is village membership. Implications for understanding the role of markets, frequent interaction with strangers, and payoffs to cooperation in daily life can help us better understand cross-cultural variation in pro-social behavior.

We experimentally test different rule-based contribution mechanisms in a repeated 4-player public goods game with endowment heterogeneity and compare them to a VCM, distinguishing between a random and an effort-based allocation of endowments. We find that endowment heterogeneities limit the efficiency gains from these rule-based contribution schemes under random allocation. Under effort-based allocations, substantial efficiency gains relative to a VCM occur. These are largely driven by significant reductions of contributions in VCM, while the rule-based mechanisms generate stable efficiency levels, even though falling short in realizing the maximal efficiency gains. Our results indicate that the procedure of endowment allocation impacts the perception of what constitutes a fair burden sharing.

In experiments with two-person sequential games we analyze whether responses to favorable and unfavorable actions depend on the elicitation procedure. In our “hot” treatment the second player responds to the first player's observed action while in our “cold” treatment we follow the “strategy method” and have the second player decide on a contingent action for each and every possible first player move, without first observing this move. Our analysis centers on the degree to which subjects deviate from the maximization of their pecuniary rewards, as a response to others’ actions. Our results show no difference in behavior between the two treatments. We also find evidence of the stability of subjects’ preferences with respect to their behavior over time and to the consistency of their choices as first and second mover.

Numerous experiments have shown that people often engage in third-party punishment (3PP) of selfish behavior. This evidence has been used to argue that people respond to selfishness with anger, and get utility from punishing those who mistreat others. Elements of the standard 3PP experimental design, however, allow alternative explanations: it has been argued that 3PP could be motivated by envy (as selfish dictators earn high payoffs), or could be influenced by the use of the strategy method (which is known to influence second-party punishment). Here we test these alternatives by varying the third party’s endowment and the use of the strategy method, and measuring punishment. We find that while third parties do report more envy when they have lower endowments, neither manipulation significantly affects punishment. We also show that punishment is associated with ratings of anger but not of envy. Thus, our results suggest that 3PP is not an artifact of self-focused envy or use of the strategy method. Instead, our findings are consistent with the hypothesis that 3PP is motivated by anger.

This paper studies whether and how strategy revision opportunities affect levels of collusion in indefinitely repeated two-player games. Consistent with standard theory, we find that such opportunities do not affect strategy choices, or collusion levels, if the game is of strategic substitutes. In games of strategic complements, by contrast, revision opportunities lead to more collusion. We discuss alternative explanations for this result.

We use data from experiments on finitely repeated dilemma games with fixed matching to investigate the effect of different types of information on cooperation. The data come from 71 studies using the voluntary contributions paradigm, covering 122 data points, and from 18 studies on decision-making in oligopoly, covering another 50 data points. We find similar effects in the two sets of experimental games. We find that transparency about what everyone in a group earns reduces contributions to the public good, as well as the degree of collusion in oligopoly markets. In contrast, transparency about choices tends to lead to an increase in contributions and collusion, although the size of this effect varies somewhat between the two settings. Our results are potentially useful for policy making, because they provide guidance on the type of information to target in order to stimulate or limit cooperation.

This study clarifies the types of motives that are important as a source of cooperation in a linear public goods experiment. Our experimental design separates contributions into those due to confusion, one-shot motives (which includes altruism, warm-glow, inequality aversion, and conditional cooperation), and multi-round motives (which includes a strategic motive under incomplete information, a failure of backward induction, and reciprocity). The experiment reveals that multi-round motives plays an important role in driving cooperative behavior. Confusion and one-shot motives play a minor role.

We study the effect of group size on cooperation in voluntary contribution mechanism games. As in previous experiments, we study four- and eight-person groups in high and low marginal per capita return (MPCR) conditions. We find a positive effect of group size in the low MPCR condition, as in previous experiments. However, in the high MPCR condition we observe a negative group size effect. We extend the design to investigate two- and three-person groups in the high MPCR condition, and find that cooperation is highest of all in two-person groups. The findings in the high MPCR condition are consistent with those from n-person prisoner’s dilemma and oligopoly experiments that suggest it is more difficult to sustain cooperation in larger groups. The findings from the low MPCR condition suggest that this effect can be overridden. In particular, when cooperation is low other factors, such as considerations of the social benefits of contributing (which increase with group size), may dominate any negative group size effect.

We use a combination of theory and experiment to study the incentives for firms to share knowledge when they engage in research and development (R&D) in an uncertain environment. We consider both symmetric and asymmetric starting points with regards to the amount of initial knowledge firms have before conducting R&D and look at how differences in starting positions affect the willingness of firms to share knowledge. We investigate when and if firms find R&D cooperation beneficial and how investment in R&D is affected by the outcome of the sharing decisions. The experimental evidence shows that overall subjects tend to behave consistently with theoretical predictions for the sharing of knowledge, although leaders who are not compensated by a side payment from laggards are more willing to share than predicted by the theory, and leaders who are compensated are less willing. The data on investment suggests less investment with sharing than without, consistent with theory. Compared to exact numerical predictions, there is overinvestment or underinvestment except for symmetric firms under no sharing. All cases of overinvestment and underinvestment, regardless of sharing or not and regardless of starting positions, are well explained by smoothed-out best (quantal) responses.