Contributed talk in ALife in Social Sciences 2, Aug. 2, 2019, 11 a.m. in room USB.G.003

Fairness in Multiplayer Ultimatum Games Through Moderate Responder Selection

Fernando Santos, Daan Bloembergen

watch Publication We study the evolution of fairness in a new multiplayer version of the classical Ultimatum Game in which a group of N Proposers jointly offers a division of resources to a group of M Responders. In general, the proposal is rejected if the (average) proposed offer is lower than the (average) response threshold in the Responders group. A motivation for our work is the exchange of flexibilities between different smart energy communities, where the surplus of one community can be offered to meet the demand of a second community. We find that, in the absence of any group selection mechanism, the co-evolving populations of Proposers and Responders converge to a state in which proposals and acceptance thresholds are low, as predicted by the rational choice theory. Low proposals imply an unfair exchange that highly favors the Proposers. To circumvent this drawback, we test different committee selection rules which determine how Responders should be selected to form decision-making groups, contingent on their declared acceptance thresholds. We find that selecting moderate Responders optimizes overall fairness. Selecting the lowest-demanding Responders maintains unfairness, while selecting the highest-demanding individuals yields a worse outcome for all due to a high fraction of rejected proposals. These results provide a practical message for institutional design and the proposed model allows testing policies and emergent behaviors on the intersection between social choice theory, committee selection and fairness elicitation.