© 2018 Shimizu, Udagawa. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Risk aversion is well-known as a general and robust characteristic of people’s decision making: people are less likely to gamble when they are unsure if they will obtain the expected value of the bet made. The “peanuts effect” is, however, an exception to this general rule. The “peanuts effect,” which states that people are more willing to gamble when playing for “peanuts” (a small outcome), has been stably observed in the context of a small monetary stake. We conducted two types of experiments to verify whether the peanuts effect still occurred when the type of stakes changed. We had two main findings. On the one hand, people tended to gamble more for a qualitatively smaller value when the stake was material in nature, meaning that the “peanuts effect” occurred with a qualitatively low stake. On the other hand, people were willing to take a risk for a qualitatively larger value when the stake was a human life: this is the opposite phenomenon of the “peanuts effect.”

Second-order free riders, who do not owe punishment cost to first-order free riders in public goods games, lead to low cooperation. Previous studies suggest that for stable cooperation, it is critical to have a pool punishment system with second-order punishment, which gathers resources from group members and punishes second-order free riders as well as first-order free riders. In this study, we focus on the priority of punishment. We hypothesize that the pool punishment system that prioritizes second-order punishment is more likely to achieve cooperation than the system that prioritizes first-order punishment, because the former is more likely to obtain sufficient punishment resources. In the experiments, we compare four pool punishment systems: 1To2 (first-order punishment to second-order punishment), 2To1 (second-order punishment to first-order punishment), 1ONLY (first-order punishment only), and 2ONLY (second-order punishment only). We find that the 2To1 and 2ONLY systems can receive more support than the 1To2 and 1ONLY systems and only the 2To1 system can achieve high cooperation. However, the effect of priority of second-order punishment is observed only when the punishment ratio (PR) is low (Experiment 1), not high (Experiment 2), in which the punishment resource is relatively abundant.

Punishment of non-cooperators-free riders-can lead to high cooperation in public goods games (PGG). However, second-order free riders, who do not pay punishment costs, reduce the effectiveness of punishment. Here we introduce a "leader support system," in which one group leader can freely punish group followers using capital pooled through the support of group followers. In our experiment, participants engage in three stages repeatedly: a PGG stage in which followers decide to cooperate for their group
a support stage in which followers decide whether to support the leader
and a punishment stage in which the leader can punish any follower. We compare a support-present condition with a no-support condition, in which there is an external source for the leader's punishment. The results show that punishment occurs more frequently in the support-present condition than the no-support condition. Within the former, both higher cooperation and higher support for a leader are achieved under linkage-type leaders-who punish both non-cooperators and non-supporters. In addition, linkage-type leaders themselves earn higher profits than other leader types because they withdraw more support. This means that leaders who effectively punish followers could increase their own benefits and the second-order free rider problem would be solved.

Punishment of non-cooperators-free riders-can lead to high cooperation in public goods games (PGG). However, second-order free riders, who do not pay punishment costs, reduce the effectiveness of punishment. Here we introduce a "leader support system," in which one group leader can freely punish group followers using capital pooled through the support of group followers. In our experiment, participants engage in three stages repeatedly: a PGG stage in which followers decide to cooperate for their group; a support stage in which followers decide whether to support the leader; and a punishment stage in which the leader can punish any follower. We compare a support-present condition with a no-support condition, in which there is an external source for the leader's punishment. The results show that punishment occurs more frequently in the support-present condition than the no-support condition. Within the former, both higher cooperation and higher support for a leader are achieved under linkage-type leaders-who punish both non-cooperators and non-supporters. In addition, linkage-type leaders themselves earn higher profits than other leader types because they withdraw more support. This means that leaders who effectively punish followers could increase their own benefits and the second-order free rider problem would be solved.

Cooperation is fundamental to human societies, and one of the important paths for its emergence and maintenance is reciprocity. In prisoner's dilemma (PD) experiments, reciprocal strategies are often effective at attaining and maintaining high cooperation. In many public goods (PG) games or n-person PD experiments, however, reciprocal strategies are not successful at engendering cooperation. In the present paper, we attribute this difficulty to a coordination problem against free riding among reciprocators: Because it is difficult for the reciprocators to coordinate their behaviors against free riders, this may lead to inequality among players, which will demotivate them from cooperating in future rounds. We propose a new mechanism, institutionalized reciprocity (IR), which refers to embedding the reciprocal strategy as an institution (i.e., institutionalizing the reciprocal strategy). We experimentally demonstrate that IR can prevent groups of reciprocators from falling into coordination failure and achieve high cooperation in PG games. In conclusion, we argue that a natural extension of the present study will be to investigate the possibility of IR to serve as a collective punishment system.

囚人のジレンマ・鹿狩りゲームはそれぞれ、協力・協調の失敗を引き起こす状況として広く知られている。本研究では、これらのゲームを繰り返し行う状況下で協力・協調を導くと期待できる三つの仕組み、すなわち、①協力・協調の難易度の段階的変化、②変化の内生性、③目標値の調整、について理論・実験により考察する。これらの仕組みは、匿名性の高い現代社会において解決が難しいジレンマ、また、権力の干渉の余地の小さい国家間の問題や個人裁量の範囲内の問題にも適用可能と考えられ、それゆえ外的妥当性が高く、応用範囲も広いと考えられる。2016年度は、三つの仕組み（段階的変化、内生性、目標値調整）が鹿狩りゲームにおいて高協力を形成・維持するのにどのような効果があるのかを明らかするために集団実験を実施した。実験研究の結果、上記三つの仕組みが鹿狩りゲームの調整問題を解決するのに有効であり、かつ、多値選択型の囚人のジレンマにおける協力の失敗の解決にも有効であることがわかった。現在、成果を英文論文にまとめ投稿するための準備を行っている。

行動経済学の功績は、人々が従来の経済学で想定されている合理性からシステマティックに乖離した行動をとることを示した点にあるが、行動経済学が政策的にどのような含意を有するものであるのかに関する研究は端緒についたばかりである。その中でも有力な傾向の一つがパターナリズムへの注目であり、従来の自由放任主義に対する反省がこの領域においても始まりつつある。なかでもリバタリアン･パターナリズムの新しさは、個人の選択肢を狭めないことで従来のパターナリズムのもつ強制的な性格を払拭しつつ、人々が気付かないうちに緩やかに望ましい方向へと誘導しようとする点にある。本研究はこの動向の中でも最も注目すべきＣ．サンスティーンとＲ．セイラーによるリバタリアン･パターナリズムを素材とする。リバタリアン・パターナリズムとは、人々の選択の自由を尊重しつつも、人々の選択を厚生改善の方向へと誘導（ナッジ）する政策を構想する規範理論上の立場であり、誘導（ナッジ）に際しては行動経済学の知見を利用する。　彼らが、実証研究を超えて行動経済学を政策提言の領域に利用する以上、規範理論との対話を回避することはできない。本研究の第一の特徴は、実証理論家と規範理論家とからなる共同研究であり、実証理論の規範的意義、規範理論の実証的意義についての検討を行うことを目的としている。この目的のために、本研究は規範理論家から提出されたリバタリアン・パターナリズムへの疑問を実証によって確かめるという手法を採っており、この点に本研究の第二の特徴がある。具体的には、本研究は、リバタリアン・パターナリズムの堅牢性の調査を目的としている。リバタリアン・パターナリズムは、暗黙のうちに、「人々は誘導されたとしても、自分にとって結果がよければ、当人の厚生は向上する」という想定を行っている。しかし、この想定が妥当であるとしてもそれは一回限りのものではないか、誘導されていたことを知らされたならば人々の厚生は減少し別の行動様式を模索するのではないか。本研究の出発点はこの疑念にある。すなわち、リバタリアン・パターナリズムは秘教的な性格を有しており、人々に誘導の事実を知られた途端にその効果は薄れるのではなかろうか。もしそうであるならば、誘導という手法は、人々の行動の公共的なコントロールの手段としてそれほど有効ではないことになる。この仮説を実験により検討することが本研究の目的である。　本研究は、その準備作業として、2012年度より実験デザインの構築に着手し、2013年度にパイロット実験を行った。同実験においては、第一段階として実際にナッジ政策が用いられるような状況下で人々の選択を誘導し、第二段階として誘導していたことを告知し、第一段階での選択を変更する希望があるのかを調査した。さらに、変更希望の有無や程度（支払意思額）と人々が社会的決定に対して持つ「規範意識」との関係について検討した。　予算の制約から、回答者数(約700人)は十分なものではなく、また質問数も制限されたが、いくつかの興味深い傾向を読みとることができた。第一に、10～20%の人々は、自分が操作されていたことを知ると、それが結果的に自分あるいは社会とって良い選択であってもその選択を変更すること。第二に、選択変更には人々の規範意識（リバタリアニズム、パターナリズム、民主的手続き主義）が関連していること、である。

本特定課題研究費によって、沖縄現地で二回にわたる資料収集が可能になった。その成果は、「米軍占領下における通貨切替が沖縄経済社会に及ぼした影響について」という論文となった。この論文は、科研費研究「経済制度の補完性と経済調整の安定性との関連の研究」（代表者：京都大学経済学研究科宇仁宏幸教授）の中の1部なす論文として、2004年4月に発行される予定である。

As H.A. Simon pointedout, the “rationality” of human beings is not perfect. He called therationality of actual human beings as “procedural rationality.” Today, it ismore often called “bounded rationality,” but there is not much differencebetween the two in substance. What is significant is that human beings areengaged in economic activities taking various limits as a given. Shiozawa(1990) called the bounds as 1) limits of vision; 2) limits of rationality and3) limits of influences. Human beings with those bounds are unable to grasp theworld perfectly and the thinking and cognitive faculty is limited. To achieve ourobjectives, we have to take various steps learning by mistakes. However, we,despite such limitations and bounds, choose our actions and live our dailylives without making serious mistakes. Usually our actions are not so muchhindered by the above-mentioned limits and we live our daily lives as if we arenot aware of those limits. Such a situation is made possible by a patternedbehavior called institutions, customs and habits. (Institutions, customs andhabits respectively have different nuances, and hereinafter the term “institutions”shall be used to signify people’s patterned behaviors except in special cases).Owing to such “institutions”, we can avoid fretting over unlimited options onone hand, and on the other, can continue to live our lives without encounteringserious inconveniences. Institutionshave two major characteristics, 1) self-enforcement and 2) self-sustenance. Inother words, people are “willingly (accepting it as a given)” and “repeatedly”follow “institutions”. “Comparative Institutional Analysis (CIA)” is an attemptthat has been made by Masahiko Aoki and others to grasp those “institutions” ina uniform manner as Nash equilibrium of the game. In this article, I shall, bychiefly focusing on CIA, analyze how evolutionary game theory accounts for thegenesis of “institutions” and examine its effectiveness.