Comparison between the expected payoff of the three types of fairness versus the observed experimental payoff for each endowment in both equal and unequal treatments.

a. Contribution fairness: in this case fairness is defined by equal contributions, where each participant is expected to contribute 1/6 of the common pot independently of their initial endowment. This definition yields particularly negative results for the most vulnerable participants, those that start with 20 €, who do not get any reward at all. We observe that in this case these participants prefer to keep part of their endowment so they have a chance to earn something. On the other hand, the rest of the groups contribute above the fair 20 € contribution. b. Payoff fairness: in this case fairness is defined by equal payoffs, where each participant is expected to receive the same payoff (20 €) independently of their initial endowment. This fairness forces the participants to end up with the same reward, that entails an increase of the experimental payoff differences. c. Relative fairness: in this third case we define fairness when all participants contribute half of their initial endowment, therefore, in this definition we expect to observe the same inequalities as before at the end of the game. Instead, we observe that in our experiments the inequality between the richest and the poorest increase.