Kohmei Makihara

Associate faculty , Faculté d'économie et de gestion (FEG) , University of Copenhagen

Makihara
Status
Postdoctoral fellow
Research domain(s)
Game theory and social networks
Thesis
2025, Aix-Marseille Université
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Contact
kohmei.makihara[at]univ-amu.fr
Website
https://sites.google.com/view/kohmeimakihara/home
Abstract We consider public goods games with heterogeneous players interacting on a network and investigate how shocks to players' characteristics and changes in interaction patterns influence individual and total contributions. We introduce a linear system associated to the initial game, in which heterogeneity in players' characteristics is removed and interactions between players are reversed, and show that what matters in determining the effects of a shock on contributions is the sign of the coordinates of its unconstrained solution. When players are identical, we demonstrate that positive shocks on active players increase contributions, while positive shocks on strictly inactive players decrease them, contrary to intuition. We also identify a subset of players, called neutral players, who exert no influence on total contributions. Furthermore, we provide precise formulas for the change in total contributions following various types of shocks, and provide conditions to determine whether the shock will have positive or negative consequences on contributions. We show that these conditions always rely on the sign of the associated problem's unconstrained solution coordinates of the players impacted by the shock.
Keywords Comparative Statics, Heterogeneous Players, Public goods
Publication HAL Google Scholar
Abstract We consider public goods games played on a potentially non-symmetric network and provide comparative statics results on individual and aggregate contributions, as well as on the effect of transfers between players. We show that, contrary to the case of the complete and symmetric network, a positive shock on a player can have adverse consequences. First, it could actually decrease this player's contribution, unless the interaction matrix is a P-matrix. Second, a positive shock on a contributing player increases aggregate contributions, but a positive shock on a non-contributing player will decrease aggregate contributions, even if the player who benefited from the positive shock increases his own contribution. In each case we provide simple conditions to determine whether a positive shock will have positive or negative consequences on contributions, by looking at the unconstrained solution of an alternative, associated game. The sign of the coordinates of this solution determines the effect of a shock. With this in hand, we further show that the aggregate neutrality result of Andreoni [1990] regarding transfers between players generally does not hold on non-symmetric networks and provide conditions for it to hold. Finally, as an application of previous results, we consider introducing agents that follow Kantian moral principles and show that, depending on their position in the network, the presence of Kantian agents can, counter-intuitively, lead to a decrease in aggregate contributions.
Keywords Public goods, Network, Comparative Statics, Kantian players
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