The influence of evolutionary selection schemes on the iterated prisoner's dilemma

Many economic and social systems are essentially large multi-agent systems. By means of computational modeling, the complicated behavior of such systems can be investigated. Modeling a multi-agent system as an evolutionary agent system, several important choices have to be made for evolutionary operators. Especially, it is to be expected that evolutionary dynamics substantially depend on the selection scheme. We therefore investigate the influence of evolutionary selection mechanisms on a fundamental problem: the iterated prisoner's dilemma (IPD), an elegant model for the emergence of cooperation in a multi-agent system. We observe various types of behavior, cooperation level, and stability, depending on the selection mechanism and the selection intensity. Hence, our results are important for (1) The proper choice and application of election schemes when modeling real economic situations and (2) assessing the validity of the conclusions drawn from computer experiments with these models. We also conclude that the role of selection in the evolution of multi-agent systems should be investigated further, for instance using more detailed and complex agent interaction models

Conflict and Cooperation in Long-Term Contracts

This Article uses the techniques of modern decision analysis and game theory to analyze the decisionmaking strategies of parties to long-term commercial contracts. Most parties to long-term contracts initially allocate the risks of future contingencies and agree – either explicitly or implicitly – to adjust this initial risk-allocation scheme if unanticipated events occur. Once contract risks are initially distributed, however, each party\u27s self-interest may compel them to evade their responsibility rather than adjust cooperatively as originally agreed. Visualizing the interactions between contracting parties as an iterated prisoner\u27s dilemma, the Author attempts to clarify the dynamics of this adjustment process. Professor Scott employs a game theoretic model to demonstrate that two polar behavioral patterns – either conflict or cooperation – would dominate if parties were unable to bargain over adjustment. However, this choice may not occur, he suggests, because even parties that are precluded from negotiating each adjustment option, nevertheless can communicate their intentions to each other. Under these conditions, a cooperative equilibrium will emerge so long as one of the parties commits to a strategy of conditional cooperation before the first adjustment is necessary. Professor Scott notes that in more realistic contractual situations, some breakdowns in patterns of mutual cooperation are inevitable. In actual contract settings, substantial problems of information and enforcement may threaten the parties\u27 efforts to realize a cooperative equilibrium. Nevertheless, he concludes that parties in continuing relationships can invoke various legal and extralegal mechanisms to reduce these information and enforcement deficits and strengthen the existing matrix of social and contractual norms

Influence of Supply Chain Network Topology on the Evolution of Firm Strategies

This study investigates the influence of the topological structure of a supply chain network (SCN) on the evolution of cooperative and defective strategies adopted by the individual firms. First, a range of topologies representative of SCNs was generated using a fitness-based network growth model, which enabled cross comparisons by parameterising the network topologies with the power law exponent of their respective degree distributions. Then, the inter-firm links in each SCN were considered as repeated strategic interactions and were modelled by the Prisoner’s Dilemma game to represent the self-interested nature of the individual firms. This model is considered an agent-based model, where the agents are bound to their local neighbourhood by the network topology. A novel strategy update rule was then introduced to mimic the behaviour of firms. In particular, the heterogeneously distributed nature of the firm rationality was considered when they update their strategies at the end of each game round. Additionally, the payoff comparison against the neighbours was modelled to be strategy specific as opposed to accumulated payoff comparison analysis adopted in past work. It was found that the SCN topology, the level of rationality of firms and the relative strategy payoff differences are all essential elements in the evolution of cooperation. In summary, a tipping point was found in terms of the power law exponent of the SCN degree distribution, for achieving the highest number of co- operators. When the connection distribution of an SCN is highly unbalanced (such as in hub and spoke topologies) or well balanced (such as in random topologies), more difficult it is to achieve higher levels of co-operation among the firms. It was concluded that the scale-free topologies provide the best balance of hubs firms and lesser connected firms. Therefore, scale-free topologies are capable of achieving the highest proportion of co- operators in the firm population compared to other network topologies

The role of dysfunctional expectation persistence in psychopathology

In the literature, expectations are seen as core elements influencing and directing human behavior. There are many different models underlying this, such as the well-known expectancy–value theories. The past few decades have seen increased interest in analyzing the role of these theories in psychotherapy. On one hand, scholars have found increasingly convincing evidence of the impact of expectations on treatment success (i.e., placebo-effect research). On the other hand, the question has arisen whether people with mental disorders differ in the content of their expectations as well as in their processing mechanisms. The ViolEx model is one of the first expectation models that has been applied to the mechanisms of psychopathology and psychotherapy. It appears that people with mental disorders not only show a greater amount of dysfunctional expectations but also that those expectations are more persistent than in people without a mental disorder. In addition to other mechanisms, the concept of “cognitive immunization” has been suggested as responsible for the maintenance of dysfunctional expectations. First, researchers have found evidence for the link between cognitive immunization (i.e., expectation persistence after an expectation-disconfirming experience) and psychopathology. For this dissertation, the process of cognitive immunization, as a relatively new concept, was analyzed in detail, with the goal of developing interventions and reducing cognitive immunization processes. In the first study, the concept of cognitive immunization was analyzed in an experimental design (N = 102). Social expectations were induced and violated, and the expectation adaptation was hypothesized to differ between micro-interventions, including an expectation- focused psychological intervention (EFPI). The EFPI group showed significantly greater variability in their expectations and, thus, lower rates of cognitive immunization compared to the other groups. Second, the complexity of the implicit operationalization of cognitive immunization through experimental designs showed the need for efficient (self-rating) instruments. Therefore, a self-rating questionnaire, the Immunization Scale (IMS), has been developed. The IMS was validated through exploratory (N = 230) and confirmatory (N = 299) factor analyses, resulting in a 23-item questionnaire. In the third study, the EFPI was tested for its effectiveness in reducing cognitive immunization, measured with the IMS. Therefore, an online longitudinal randomized controlled design was developed for people with mild depressive and/or anxiety symptoms (N = 128). Cognitive immunization was correlated with psychopathology, and the EFPI group showed a significant reduction in the cognitive immunization level. Lastly, and based on the third study, a protocol paper was written for a large-scale psychotherapeutic study that analyzes the effectiveness of cognitive behavioral therapy (CBT) with the integration of EFPIs in people with diagnosed depression compared to standard CBT without special focus on expectations. This dissertation provides a validated questionnaire to analyze cognitive immunization processes and their link to psychopathology. It offers initial evidence of EFPIs’ effectiveness in reducing cognitive immunization in people with psychopathological symptoms. Practical and research implications are discussed

Emergence and Collapse of Peace with Friend Selection Strategies

A society consisting of agents who can freely choose to attack or not to attack others inevitably evolves into a battling society (a \'war of all against all\'). We investigated whether strategies based on C. Schmitt\'s concept of the political, the distinction of a friend and an enemy, lead to the emergence and collapse of social order. Especially, we propose \'friend selection strategies\' (FSSs), one of which we called the \'us-TFT\' (tit for tat) strategy, which requires an agent to regard one who did not attack him or his \'friends\' as a \'friend\'. We carried out evolutionary simulations on an artificial society consisting of FSS agents. As a result, we found that the us-TFT results in a peaceful society with the emergence of an us-TFT community. In addition, we found that the collapse of a peaceful society is triggered by another FSS strategy called a \'coward\'.Community, Carl Schmitt, a Friend and an Enemy, Tit for Tat, Coward, Evolutionary Simulation

Evolutionary Games in Complex Topologies: Interplay between Structure and Dynamics

En este estudio exploramos la interrelación entre la estructura subyacente de una cierta población de individuos y el resultado de la dinámica que está teniendo lugar en ella, específicamente, el Dilema del Prisionero. En la primera parte de este trabajo analizamos el caso de una topología estática, en la que la red de conexiones no cambia en el tiempo. En la segunda parte, desarrollamos dos modelos para crecer redes, donde dicho crecimiento esta íntimamente relacionado con la dinámica

On the Nature, Modeling, and Neural Bases of Social Ties

This paper addresses the nature, formalization, and neural bases of (affective) social ties and discusses the relevance of ties for health economics. A social tie is defined as an affective weight attached by an individual to the well-being of another individual (‘utility interdependence’). Ties can be positive or negative, and symmetric or asymmetric between individuals. Characteristic of a social tie, as conceived of here, is that it develops over time under the influence of interaction, in contrast with a trait like altruism. Moreover, a tie is not related to strategic behavior such as reputation formation but seen as generated by affective responses. A formalization is presented together with some supportive evidence from behavioral experiments. This is followed by a discussion of related psychological constructs and the presentation of suggestive neural findings, based on the existing literature. We conclude with some suggestions for future research. Publication forthcoming in 'On the Nature, Modeling and Neural Bases of Social Ties', Daniel E. Houser and Kevin A. McCabe (eds), Neuroeconomics, Advances in Health Economics and Health Services Research, Emerald Insight Publishing

College Dating Couples\u27 use of Conflict Management during a Prisoner\u27s Dilemma Task: An Exploratory Study

Dating violence that occurs in young college-aged couples is unique when compared to other types of violence. Aggression occurring in these couples is often bidirectional, highly impacted by situational stressors, and perpetrated by both males and females at relatively equal rates. Most importantly, dating aggression occurs within a developmental context when individuals are attempting to balance autonomy and intimacy within their relationships. However, little is known about conflict management within dating couples or if conflict management processes differ substantially for aggressive and non-aggressive dating couples. Although there has been extensive research in marital processes in conflict, only recently have researchers argued the need for conflict management of young, dating couples to be studied in a dynamic way (Capaldi, Kim, & Shortt, 2007). For this study, a computer administered version of the iterated Prisoner\u27s Dilemma game was used as a tool for elicitation and observation of conflict behavior of young, dating couples. Specific in-game responding including negative escalation (termed defection spirals), cooperation, and repair were examined both quantitatively and qualitatively. In addition to the Prisoner\u27s Dilemma game, participants completed questionnaires regarding personal history, current mood, and information on their dating relationship. A cross-sectional sample of college couples (N = 40 couples) was used and group membership (either aggressive or non-aggressive) was determined by endorsement of items on the Revised Conflict Tactic Scales (Straus, Hamby, Boney-McCoy, & Sugarman, 1996). Findings suggest aggressive and non-aggressive couples\u27 perceptions and approach to the Prisoner\u27s Dilemma game differed significantly. Primary hypotheses regarding differences between groups on the use of defection, cooperation, and repair over time (Group x Time interactions) were not supported by the data. However, aggressive and non-aggressive couples differed significantly on their use of defection and cooperation responses. For example, aggressive couples used more defection responses throughout the Prisoner\u27s Dilemma game while non-aggressive couples used more cooperative responses. Descriptive analysis of game patterns by group indicated differing patterns for aggressive and non-aggressive couples. In addition, exploratory hypotheses examining the relationship between the Prisoner\u27s Dilemma game and aggressiveness towards one\u27s partner were significant, thus, adding to the literature in this area. Implications of these findings and future research are discussed