DOI: 10.5061/dryad.x0k6djhnq
title: Data and code from: Cooperation and coordination in heterogeneous populations

description: One landmark application of evolutionary game theory is the study of
 social dilemmas. This literature explores why people cooperate even when
 there are strong incentives to defect. Much of this literature, however,
 assumes that interactions are symmetric. Individuals are assumed to have
 the same strategic options and the same potential payoffs. Yet many
 interesting questions arise once individuals are allowed to differ. Here,
 we study asymmetry in simple coordination games. In our setup, human
 participants need to decide how much of their endowment to contribute to a
 public good. If a group’s collective contributions reach a pre-defined
 threshold, all group members receive a reward. To account for possible
 asymmetries, individuals either differ in their endowments or their
 productivities. According to our theoretical equilibrium analysis, such
 games tend to have many possible solutions. In equilibrium, group members
 may contribute the same amount, different amounts, or nothing at all.
 According to the behavioral experiment, however, humans favor the
 equilibrium in which everyone contributes the same proportion of their
 endowment. We use these experimental results to highlight the nontrivial
 effects of inequality on cooperation, and we discuss to which extent
 models of evolutionary game theory can account for these effects.
description: Experimental setting:  There are five
 treatments: full equality, moderate endowment inequality, strong endowment
 inequality, moderate productivity inequality, and strong productivity
 inequality. Each participant is assigned to one treatment only. Each
 treatment includes two games: participants play Game 1 first and then Game
 2. At the beginning of Game 1, players are randomly matched in pairs,
 where in each pair one player is assigned to Role 1 and the other is Role
 2. They then play 20 rounds of the asymmetric threshold public goods game
 (TPGG). Throughout a game, the pair of players and their roles do not
 change. The players receive their fixed endowments and independently
 decide an integer amount out of their endowment to contribute to a public
 good. A player's effective contribution is their contribution
 multiplied by their individual productivity factor. If the sum of the
 players' effective contributions exceeds a threshold, then both of
 them receive a reward. The payoff in each round  is the sum of the
 remaining amount of the initial endowment and the reward if the threshold
 is reached. At the end of each round, players receive information about
 the contributions and payoffs of themselves and their partners, as well as
 the total effective contribution (that is, whether they have reached the 
 threshold). After Game 1, players engage in Game 2. Again, they play 20
 rounds of the asymmetric TPGG but now with a different partner and in the
 opposite role. Finally, players are asked to finish a questionnaire on
 what they consider to be the fair contribution pattern.
 The experiment was conducted in the computer labs of Beijing
 Normal University. All the 558 subjects were undergraduates and graduates
 recruited from Beijing Normal University. The interactions were anonymous,
 and took place via computers.The experimental platform software was built
 using o-Tree (version 5.3).
description: Please refer to the ReadMe file.