Department of Value and Decision Science, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro, Tokyo 152-8552, Japan.
J Theor Biol. 2010 May 7;264(1):143-53. doi: 10.1016/j.jtbi.2009.12.030. Epub 2010 Jan 11.
Collective behavior is theoretically and experimentally studied through a public goods game in which players contribute resources or efforts to produce goods (or pool), which are then divided equally among all players regardless of the amount of their contribution. However, if goods are indivisible, only one player can receive the goods. In this case, the problem is how to distribute indivisible goods, and here therefore we propose a new game, namely the "rotating indivisible goods game." In this game, the goods are not divided but distributed by regular rotation. An example is rotating savings and credit associations (ROSCAs), which exist all over the world and serve as efficient and informal institutions for collecting savings for small investments. In a ROSCA, members regularly contribute money to produce goods and to distribute them to each member on a regular rotation. It has been pointed out that ROSCA members are selected based on their reliability or reputation, and that defectors who stop contributing are excluded. We elucidate mechanisms that sustain cooperation in rotating indivisible goods games by means of evolutionary simulations. First, we investigate the effect of the peer selection rule by which the group chooses members based on the players reputation, also by which players choose groups based on their reputation. Regardless of the peer selection rule, cooperation is not sustainable in a rotating indivisible goods game. Second, we introduce the forfeiture rule that forbids a member who has not contributed earlier from receiving goods. These analyses show that employing these two rules can sustain cooperation in the rotating indivisible goods game, although employing either of the two cannot. Finally, we prove that evolutionary simulation can be a tool for investigating institutional designs that promote cooperation.
通过公共物品博弈对集体行为进行理论和实验研究，在该博弈中，玩家贡献资源或努力来生产（或汇集）商品，然后无论其贡献多少，这些商品都会平均分配给所有玩家。然而，如果商品是不可分割的，那么只有一名玩家可以获得商品。在这种情况下，问题是如何分配不可分割的商品，因此我们提出了一种新的游戏，即“旋转不可分割商品游戏”。在这个游戏中，商品不是通过分割而是通过定期轮换来分配的。一个例子是旋转储蓄和信贷协会（ROSCAs），它们遍布世界各地，是为小额投资筹集储蓄的有效非正式机构。在 ROSCA 中，成员定期贡献资金来生产商品，并按定期轮换向每个成员分配商品。有人指出，ROSCAs 成员是根据其可靠性或声誉来选择的，而停止贡献的违约者则被排除在外。我们通过进化模拟阐明了维持旋转不可分割商品游戏中合作的机制。首先，我们研究了同伴选择规则的效果，即小组根据玩家的声誉选择成员，玩家也根据他们的声誉选择小组。无论采用哪种同伴选择规则，旋转不可分割商品游戏中的合作都无法持续。其次，我们引入了没收规则，即禁止以前没有贡献的成员获得商品。这些分析表明，采用这两个规则可以维持旋转不可分割商品游戏中的合作，尽管只采用其中一个规则则无法维持合作。最后，我们证明进化模拟可以成为研究促进合作的制度设计的工具。
