The Individual Behavior in a Public Goods game

Generally, with a standard linear public goods game, one observes at the aggregate level that contributions lay between the Nash equilibrium and the social optimum and decrease over time with an end-effect.Our purpose is to see whether these general aggregate results remain available at the group and at the individual levels. To do so, we formed six groups of four persons and made them play a public goods game. At the aggregate level, we find that our results correspond almost to the standard experimental findings in literature.Using the classification of Isaac et al. (1984), we find that at the group level, only two groups adopt the standard behavior and only two groups present a behavior similar to what we obtain at the aggregate level. At the individual level, we compare contributions over time of each subject to the group and the aggregate results and classify them into types. Only in one of the 6 groups individuals adopt an homogeneous behavior. In the five other groups, individuals have different behaviors.