報酬、對手類型在重複信任賽局中對決策的影響

Abstract

本研究的目的在探討在重複信任賽局中兩種不同的角色（信任者、受益者）、對手類型與金額大小對信任與回報決策的影響。74名參與者隨機被指配至兩種角色之中，他們會遭遇不同的對手類型（信任者：信任、利他、互惠、自利、不信任。受益者：回報利潤、利他、互惠、自利、獨吞）與2種報酬大小（高、低）的信任賽局共250次，其中前10局為基準線的量測，沒有對類型的操弄。實驗結果發現，在小金額的情況下，信任者在前一局中對對手的貢獻金額越高，則受益者給他的回報金額也越大(平均1.394，相對於baseline的1.184，上升了21%)；在大金額的情況下，受益者回報的金額皆維持在本金以下，且除了對獨吞的信任者有較低的回報外(0.68)，回報的金額不因信任者給比率不同，而有顯著的差異(0.88至1.08)。另一方面，若得知受益者上一局中對手回報的比率越高，信任者在給他貢獻時比率也會由0.328上升至0.719，隨上一局給對手的金額比率上升而上升，高於本金與利潤的一半金額後，信任者的貢獻金額則不再隨著受益者的回報金額而上升，顯示信任者和受益者決策時的衡量因素並不相同。不論是信任者或是受益者，當決策涉及較大金額的金錢時，都會顯現出較自利的行為。

The effects of the amount of payoff (small vs. large) and the information about playmate’s previous giving behavior were examined on repeated trust games. Seventy-nine college students played the role of trustor or receiver in 250 trials of trust games in which the first 10 trials served as the baseline measure and the data from the remaining 240 trials were grouped into 6 blocks. Money trustors gave to the receivers and money receivers return to the trustors were subject to 6 (block) × 5 (player type) × 2 (payoff) analysis of variance with repeated measures. Data show that participants would punish those who give or return very little money to their playmates. But how much they would give or return depends on how generous the other players were presented to them. For trustors, the money they gave to the other players increased linearly with the generosity of the receiver in the previous game. For receivers, how much money they would return to their trustors was a function of both the trustor’s generosity in the previous game and the amount of the money the received from the current trustor. When the amount of money given to them was large, the receiver would return about 88% of the money they obtained from the trustor, and this amount was not affected by how generous the trustor was to people in the previous trial. When the amount of money they received from the trustor was small, the receiver would return about 1.18% of the money trusted to them, and the amount of return would increase quickly as a function of trustor’s generosity from 0 to 50% and then level off from 50% to 100%. When mapping results to the baseline, it appears that trustor’s and receiver’s decisions are based on a “fair world” assumption. Keyword: trust game, payoff, indirect reciprocity, repeated games, decision-making, and information about past behavior.