Intergroup Prisoner's Dilemma Research Articles

Prior interaction, identity, and cooperation in the Inter-group Prisoner's Dilemma

This paper studies theoretically and experimentally how success in prior interaction affects cooperation in the one-shot Inter-group Prisoner's Dilemma (IPD). We develop a model of the IPD that incorporates group-contingent social preferences and bounded rationality to derive conditions under which an increase in pro-social concerns for an out-group will increase cooperation. We then report an experiment that shows the cooperation rate increases from 8 percent in a baseline one-shot IPD to 42 percent when the IPD is preceded by a coordination game played by members of the two groups. A post-experiment survey and chat coding results using a natural language classification game both show that successful prior interaction increases individuals’ concerns for their out-group.

Editorial: Parochial Altruism: Pitfalls and Prospects.

Editorial: Parochial Altruism: Pitfalls and Prospects.

“Ingroup love” and “outgroup hate” in intergroup conflict between natural groups

We report on two studies investigating the motivations (“ingroup love” and “outgroup hate”) underlying individual participation in intergroup conflict between natural groups (fans of football clubs, supporters of political parties), by employing the Intergroup Prisoner's Dilemma Maximizing-Difference (IPD-MD) game. In this game group members can contribute to the ingroup (at a personal cost) and benefit ingroup members with or without harming members of an outgroup. Additionally, we devised a novel version of the IPD-MD in which the choice is between benefiting ingroup members with or without helping members of the outgroup. Our results show an overall reluctance to display outgroup hate by actively harming outgroup members, except when the outgroup was morality-based. More enmity between groups induced more outgroup hate only when it was operationalized as refraining from help.

The effects of individual and context on aggression in repeated social interaction

In two studies using variations of the Prisoner's Dilemma game, we explore the impact of individual traits and social context on aggressive behavior. In the first study, we compared defection rates in the Iterated Prisoner's Dilemma when participants were presented with a payoff matrix (Description condition) or learned payoffs through experience (Experience condition). Interpersonal trust and maximizing tendency led to relatively less defection in the Description condition than in the Experience condition, demonstrating that individual characteristics manifest differently depending on the information available to decision-makers. In the second study, we employed a new game paradigm, the Intergroup Prisoner's Dilemma with Intragroup Power Dynamics, to examine the way that power motives influence extreme aggressive behavior. We discovered that certain individuals exhibit very high levels of defection, but only when they play with particular combinations of predefined strategies, further suggesting how the confluence of individual factors and context can induce aggression.

Maximization of Absolute vs. Relative Gains in Intergroup Conflicts

What motivates individual self-sacrificial behavior in intergroup conflicts? Is it the altruistic desire to help the ingroup or the aggressive drive to hurt the outgroup? This paper introduces a new game paradigm, the Intergroup Prisoner's Dilemma - Maximizing Difference (IPD-MD) game, designed specifically to distinguish between these two motives. The game involves two groups. Each group member is given a monetary endowment and can decide how much of it to contribute. Contribution can be made to either of two pools, one which benefits the ingroup at a personal cost, and another which, in addition, harms the outgroup. An experiment demonstrated that contributions in the IPD-MD game are made almost exclusively to the cooperative within-group pool. Moreover, pre-play intragroup communication increases intragroup cooperation but not intergroup competition. These results are compared with those observed in the Intergroup Prisoner's Dilemma (IPD) game, where group members' contributions are restricted to the competitive between-group pool.

“In-Group Love” and “Out-Group Hate” as Motives for Individual Participation in Intergroup Conflict

What motivates individual self-sacrificial behavior in intergroup conflicts? Is it the altruistic desire to help the in-group or the aggressive drive to hurt the out-group? This article introduces a new game paradigm, the intergroup prisoner's dilemma-maximizing difference (IPD-MD) game, designed specifically to distinguish between these two motives. The game involves two groups. Each group member is given a monetary endowment and can decide how much of it to contribute. Contribution can be made to either of two pools, one that benefits the in-group at a personal cost and another that, in addition, harms the out-group. An experiment demonstrated that contributions in the IPD-MD game are made almost exclusively to the cooperative, within-group pool. Moreover, preplay intragroup communication increases intragroup cooperation, but not intergroup competition. These results are compared with those observed in the intergroup prisoner's dilemma game, in which group members' contributions are restricted to the competitive, between-group pool.

Cantankerous Cooperation: Democracies, Authoritarian Regimes, and the Prisoner's Dilemma

One of the most important debates in the field of international relations is over the effect of regime type on militarized conflict. This debate, however, has rarely extended to how regime type influences other aspects of foreign policy. Using a computer simulated intergroup prisoner's dilemma, we investigate whether democratic decisionmaking groups are more cooperative than authoritarian decisionmaking groups. We argue that differences between cooperation tendencies of groups can be explained by the structure of the decision process. Repeated simulations show that democracies tend to be more consistent in their decisions in comparison to authoritarian groups. Implications for international relations theory and policy are discussed.

Nonparametric Analysis of Longitudinal Binary Data: An Application to the Intergroup Prisoner's Dilemma Game

The intergroup prisoner's dilemma game was suggested by Bornstein (1992, Journal of Personality and Social Psychology. 7, 597–606) for modelling intergroup conflicts over continuous public goods. We analyse data of an experiment in which the game was played for 150 rounds, under three matching conditions. The objective is to study differences in the investment patterns of players in the different groups. A repeated measures analysis was conducted by Goren and Bornstein (1999, Games and Human Behaviour: Essays in Honor of Amnon Rapoport, pp. 299–314), involving data aggregation and strong distributional assumptions. Here we introduce a nonparametric approach based on permutation tests. Two new measures, the cumulative investment and the normalised cumulative investment, provide additional insight into the differences between groups. The proposed tests are based on the area under the investment curves. They identify an overall difference between the groups as well as pairwise differences. A simultaneous confidence band for the mean difference curve is used to detect the games which account for any pairwise difference.

The Effects of Intragroup Communication on Intergroup Cooperation in the Repeated Intergroup Prisoner's Dilemma (IPD) Game

The intergroup prisoner's dilemma (IPD) game was played repeatedly in an attempt to distinguish the dynamic process associated with reciprocation at the intergroup level from that resulting from adaptation at the individual level. Results show that when players were not allowed to communicate with one another, they gradually learned that it does not pay to participate, but when within-group communication was allowed, the overall effect was to increase individual participation. However, this effect varied greatly in later stages of the game. In some cases, intragroup communication eliminated individual participation and rewarded the members of both teams with the mutually cooperative outcome, but in other cases, it intensified the intergroup conflict to its maximal level of full participation. The implications of these findings for conflict resolution are discussed.

Experimental study of repeated team-games

We report an experiment in which the Intergroup Prisoner's Dilemma (IPD) game was contrasted with a structurally identical (single-group) Prisoner's Dilemma (PD). The games were played repeatedly for 40 rounds. We found that subjects were initially more likely to cooperate in the IPD game than in the PD game. However, cooperation rates decreased as the game progressed and, as a result, the differences between the two games disappeared. This pattern is consistent with the hypothesis that subjects learn the structure of the game and adapt their behavior accordingly. Computer simulations based on a simple learning model by Roth and Erev (Learning in extensive-form games: Experimental data and simple dynamic models in the intermediate term, Games and Economic Behavior 8, 164–212, 1995) support this interpretation.

The Effect of Repeated Play in the IPG and IPD Team Games

Repeated interaction in integroup conflict was studied in the context of two team games: the intergroup public goods (IPG) game and the intergroup prisoner's dilemma (IPD) game. The results reveal (a) a main effect for game type; subjects were twice as likely to contribute toward their group effort in the IPG game than in the IPD game, and (b) a Game-Type × Time interaction; subjects contributed less over time in the IPD game while continuing to contribute at about the same rate in the IPG game. The second finding supports the hypothesis that subjects learn the structure of the game and adapt their behavior accordingly and is compatible with a simple learning model, which assumes that choices that have led to good outcomes in the past are more likely to be repeated in the future. A reciprocal cooperation hypothesis, which assumes that players make their choices contingent on the earlier choices of the other players, received little support.

Interindividual-Intergroup Discontinuity in the Prisoner's Dilemma Game

The present research involved an examination of interindividual-intergroup discontinuity in the context of three different generalizations of the prisoner's dilemma game (PDG). (Interindividual-intergroup discontinuity is the tendency of intergroup relations to be more competitive and less cooperative than interindividual relations.) Experiment 1 used a multi-prisoner's dilemma (MPD) game to compare interaction between three individuals with interaction between three groups. Results revealed just as much discontinuity between three players (MPD) as between two players (PDG). Experiment 2 used the approach of n-person games to examine two further generalizations from the PDG. One generalization involved the intergroup public goods (IPG) game, and the other the intergroup prisoner's dilemma (IPD) game. With both games, it was found that groups were more competitive than individuals. It was also found that discussion between groups is characterized by a higher frequency of fear and greed statements than is discussion between individuals.