Construction of a decision and learning model in repeated social dilemma games: Model evaluation using Bayesian statistical modeling

Several laboratory experiments of social dilemma game have provided robust data suggesting that the initially high cooperation rate declines as the game is repeated. However, changes in decision-making mechanisms that are responsible for this decline are not well understood. Although reinforcement learning models can explain changes in the cooperation rate from the perspective of evolution, they cannot explain the high initial cooperation rate and the subsequent decline. In this study, a decision-making model was derived from the social value orientation (SVO) model (Muto, 2006), and the expected utility of cooperation and non-cooperation was integrated into a learning model. Then, a laboratory experiment was conducted to test the model. The model comparison showed that the data were best explained by the model that considered learning from the perspective of the game’s gain structure, including the marginal per capita of return (MPCR), and the cooperation of others. The results suggested the following: (1) Altruism, which is one of the parameters of SVO has a positive main effect on cooperation, whereas equality, which is the other parameter of SVO has an effect on cooperation only through the interaction with the expectations for cooperation by others; (2) MPCR is estimated to be high at the beginning of the game, and cooperation decrease as MPCR is perceived more accurately. (3) The impact of equality accelerates the decline in cooperation when the expectations for cooperation by others fall below 50% as a result of accurately estimating the MPCR.