OSIPP Faculty Publications (July 2026)

This page lists publications submitted by OSIPP faculty members.

＜Peer-Reviewed Articles＞

Tomohiro Hosoi
Hosoi, Tomohiro, Hiroto Ito and Koji Oishi. 2026. ‘State of Civil War in the Phantom State: Integration and Fragmentation among Armed Groups in the Central African Republic since 2005’, International Journal of Afrasian Studies, 3 (1), 1-21.
https://www.afrasia.org/journal

Abstract:
The Central African Republic (CAR) has been in turmoil due to severe armed conflict since 2012. However, the patterns of integration and fragmentation of the rebel groups in the country are hardly known. This study constructs a new dataset based on official documents and news sources to give a comprehensive picture of integration and fragmentation among CAR rebels. We show five findings from the dataset. First, there are three main streams among rebels in CAR. Second, integrations among rebels are rare. Third, even if an integration occurs, it does not survive in most cases. Fourth, in contrast to the existing research, the Anti-Balaka is not a pure self-defence force. Finally, the creation of the Coalition des Patriotes pour le Changement (CPC) in 2020 is a noteworthy event in the recent political landscape of the CAR. Moreover, we suggest two mechanisms behind such observations. First, rebel leaders have loyalty toward political big men. The second is the power-balancing of rebel leaders against the government which gained international support. This research provides some new insights on the country to both scholars and practitioners.

Noriaki Matsushima
Noriaki Matsushima, Kazuki Nishikawa, Jiaying Qiu
“The effects of minimum wage regulation in inter-regional oligopoly competition”
Contemporary Economic Policy, accepted July 2026, Forthcoming.

Abstract:
The minimum wage may be seen as something that “raises labor costs and reduces profits” for firms. This study, however, uses a simple theory to show a mechanism under which, depending on conditions, a minimum wage can instead increase a firm’s profits. We consider two firms that compete in the same product market. The two firms hire workers in different regions that are geographically separated. In each region, there is almost only one large employer—effectively a monopsony labor market. As a result, each firm keeps wages low. What happens if a minimum wage is introduced in only one of the two regions? When the minimum wage sets a wage floor, the firm in the regulated region may, in some cases, face a lower marginal labor cost—the additional labor cost from hiring one more worker. This is a well-known effect in monopsony analysis. The regulated firm then increases employment and output, while its rival, competing in the same product market, is pushed to reduce output. As a result, the regulated firm may expand its market share and raise its profits. What is interesting here is that the rival firm’s costs do not change at all. As a real-world example, this framework may fit the situation in China where major assemblers competing for Apple orders (such as Luxshare Precision and Foxconn) compete under minimum wages that differ by province. The lesson from this result is also important. A minimum wage in one region raises wages for workers in that region and can, in some cases, even stimulate business activity there. At the same time, however, competition in the product market can reduce employment and production in another region. In other words, an evaluation that “there is no visible harm if we look only locally” may miss the overall effects. This study illustrates this point using a very simple theoretical model.

Naruki Notsu
Naruki Notsu, Shuko Harada, Yu Osaki
“Financial impacts of standardized system specifications: evidence from japanese municipalities”
International Tax and Public Finance (2026)
https://doi.org/10.1007/s10797-026-09986-0

Abstract:　
This paper examines whether standardized system specifications improve the fiscal efficiency of local governments. Although ICT has been widely promoted through e-government initiatives to improve government operations, the effectiveness of system standardization has received limited attention. We study Japan’s Regional Information Platform (RIP), a standardized system specification that facilitates interoperability across municipal administrative systems and weakens vendor lock-in. Building on a model of municipal procurement under switching costs, we show that standardization reduces expenditure through two channels: weakened vendor lock-in that lowers system costs, and improved cross-departmental interoperability that reduces labor input. Using variation in RIP adoption across Japanese municipalities, we estimate difference-in-differences models and find that RIP adoption substantially reduces per capita total expenditure. These findings suggest that e-government outcomes depend not only on ICT adoption itself but also on whether administrative systems are standardized and interoperable.

赤井伸郎
小川顕正・赤井伸郎（2026）「行動経済学的特性がマイナンバーカード普及に与える影響について―個票データに基づく要因分析」『日本経済研究』84, pp. 1-23.
https://www.jcer.or.jp/jcer_download_log.php?f=eyJwb3N0X2lkIjoxMzk4MzcsImZpbGVfcG9zdF9pZCI6IjEzOTgyMSJ9&post_id=139837&file_post_id=139821

概要：本稿では、マイナンバーカードの取得と行動経済学的な個人特性の関係について分析を行った。個票データを用いた分析によると、現在バイアスが強い人がマイナンバーカードの取得申請を先延ばしにしがちであること、利他性が高い人がマイナンバーカードの取得に至りやすいことのほか、一般的信頼性が高い人ほど行動変容を促すのに必要な金銭的インセンティブの金額が小さいことなどが明らかになった。以上の結果を踏まえ、非金銭的手段や個人特性を踏まえた金銭的インセンティブ設定の可能性などについて議論している。

＜Book Chapters＞

Kentaro Wani, Hinako Takata
Maiko Meguro and Yota Negishi (eds.), Histories of international legal theories in Japan: From dialogue to conversation (Manchester University Press, 2026)
https://manchesteruniversitypress.co.uk/9781526174949/

概要：本書は、13人の代表的な日本の国際法学者を軸に、100年以上にわたる日本の国際法理論の展開を体系的にたどり、西洋近代と日本固有の法的・知的伝統との緊張に日本の研究者がどのように向き合ってきたかを明らかにすることを目的とするものである。

Hinako Takata
Chapter 2: YOKOTA Kisaburo: Between value-neutrality, and internationalist, pacifist and democratic ideals (pp. 52-75)

概要：髙田が執筆した第二章は、横田喜三郎の国際法理論への貢献について分析したものであり、横田が日本の（国際）法学における純粋法学の受容のために果たした役割や、国際法と国内法の関係に関する横田の研究、そして、横田の「国際民主主義」理論をとりあげてそれぞれ検討し、最後に、横田の理論的立場の一貫性について分析した。

Kentaro Wani
Chapter 9: ISHIMOTO Yasuo: The ‘structural transformation’ of international law (pp. 194-213)

概要：和仁が執筆した第九章は、戦後第一世代の代表的な国際法学者の一人である石本泰雄(1924-2015)の国際法理論、特に彼の「国際法の構造転換」論と、同議論の中核をなす「平和と戦争の二元的構造の古典的国際法から一元的構造の現代国際法への転換」という議論について検討した。これらの議論は、戦後日本の国際法学界においてもっとも広く共有された議論の一つであり、日本の国際法学を特徴づける議論でもある。本章は、「国際法の構造転換」論を中心に石本の国際法学を検討し、それにより日本の国際法学の特徴の一端を示そうとしたものである。

＜Case Notes＞

二杉健斗「［判例研究］国際司法裁判所 イランのある種の財産事件（イラン対米国）（先決的抗弁判決・2019年2月13日））（本案判決・2023年3月30日））」国際法外交雑誌125巻1号（2026年）144-158頁

概要：本稿は、国際司法裁判所（ICJ）の「イランのある種の財産事件」（先決的抗弁判決・本案判決）の評釈である。本稿では、イラン中央銀行の「会社」該当性につき本案判決が導入した「主権的機能との連関」基準が抗弁判決と矛盾するとの批判に対し、抗弁判決は性質基準の具体的内容を既判事項とはしておらず、本案判決はその空白を補充したに過ぎないと論じる。また、本件が条約の趣旨目的を越えた管轄権拡張への謙抑を示した点を評価しつつ、多数意見による3条1項（会社の法的地位の承認）の違反の認定はその独自の有用性（effet utile）を損なうことや、収用判断において条約上の不合理性基準を一般国際法上のpolice power判断へ流用した点には法論理上の問題が残ることを指摘している。

二杉健斗「投資協定仲裁判断例研究（188）アルゼンチン経済危機に起因する最後の事案において、規制変更の恣意性が認定された事例」JCAジャーナル73巻7号（2026年）26-32頁
https://www.jcaa.or.jp/files/publishing/pdf_index00000096.pdf

概要：AES Corporation v. Argentine Republic, ICSID Case No. ARB/02/17における仲裁判断（2025年5月30日）の判例評釈である。本件はアルゼンチン経済危機（2001-2002年）に起因する紛争であるが、長期に亘って仲裁手続が停止していたことから、一連の事案の中で最後に仲裁判断が出された。本稿では、そうした時間経過による影響も含め、アルゼンチン事案全体の文脈における本件の特徴を整理するとともに、公正衡平待遇（FET）の一要素としての恣意性の解釈および判断基準、被申立国に準拠した利息の計算の問題性、安全保障例外の解釈上の特徴等を指摘した。

＜Discussion Papers＞

Naruki Notsu
Naruki Notsu, Haruaki Hirota
“Administrative Consolidation and the Cost of State Capacity”
OSIPP Discussion Paper: DP-2026-E-009, 29 June 2026
https://www.osipp.osaka-u.ac.jp/archives/DP/2026/DP2026E009.pdf

Abstract:
This paper studies how administrative consolidation affects the performance and cost of fiscal capacity. While consolidation may reduce administrative costs by exploiting scale effects, it may also disrupt the accumulated organizational resources and routines through which governments collect taxes. We examine this trade-off, focusing on Japan’s Great Heisei Municipal Mergers, a large wave of municipal consolidation in the early 2000s. Using an event-study based on a difference-in-differences design, we find that mergers reduce tax collection rates beginning in the pre-legal-merger transition period. In contrast, tax administrative costs fall only after formal consolidation, consistent with economies of scale in tax administration. We further find that tax revenue collected per unit of administrative cost increases after consolidation despite the decline in collection rates. These findings show that administrative consolidation weakens the collection margin of fiscal capacity during organizational transition, while lowering the resource cost of raising revenue enough to improve overall cost-effectiveness. The results highlight a trade-off between the operational performance and cost-effectiveness of fiscal capacity.