We recruited 541 subjects of different ages, educational level, and social status during a fair in Barcelona. The experiment consisted of multiple rounds, in which participants were randomly assigned partners and assigned randomly chosen payoff values, allowing us to study the behavior of the same subject in a variety of dyadic games including PD, SH, SG, and HG, with different payoffs. To incentivize the experimental subjects’ decisions with real material (economic) consequences, they were informed that they would proportionally receive lottery tickets (one ticket per 40 points; the modal number of tickets earned was two) to the payoff they accumulated during the rounds of dyadic games they played. The prize in the corresponding lottery was four coupons redeemable at participating neighboring stores, worth 50 euros each.

For every cluster, a column represents a player belonging to his or her corresponding cluster, whereas the four rows indicate the four average cooperation values associated with his or her (from top to bottom: cooperation in HG, SG, SH, and PD games). We color-coded the average level of cooperation for each player in each game (blue, 0.0; red, 1.0), whereas the lack of value in a particular game for a particular player is coded in white. Cluster sizes: Envious, n = 161 (30%); Pessimist, n = 113 (21%); Undefined, n = 66 (12%); Optimist, n = 110 (20%); Trustful, n = 90 (17%).

http://advances.sciencemag.org/content/2/8/e1600451.full