Research

JMP

• Kei Ikegami, Bargaining over Leasing Contracts: Strong by Privilege but Weak by Risk Aversion (New draft: March 12, 2025)
  Short Summary

  Many business transactions rely on contracts specifying transfers, making it difficult to observe how power imbalances shape agreed terms. This study introduces a bargaining model that recovers each party’s position from observed contract terms and applies it to tenant lease agreements in shopping malls. I find that when the mall holds a stronger bargaining position, it tends to forgo higher fixed rent in favor of contracts that generate more variable rent. At the same time, at such lower sales levels, recovering sufficient rent through variable components becomes difficult, making privileged mall managers more risk-averse. Simulation results show that even without accounting for changes in risk attitudes, fairer bargainings do not necessarily reduce total rent. Furthermore, when risk attitude shifts are considered, a sharp increase in variable rent could nearly triple total rent.
  Presentations

  IIOC 2025, APIOC 2024, UTMD rising star in market design, NYU seminar
  Short slide, Long slide

Publication

• Kei Ikegami, Kyohei Okumura, and Takumi Yoshikawa, A Simple, Fast, and Safe Mediator for Congestion Management, AAAI '20 (Oral and Poster presentation)
• Kei Ikegami, Ken Onishi, and Naoki Wakamori, Competition-Driven Physician-Induced Demand, Journal of Health Economics, Vol. 79, September 2021

Working Paper

• Kei Ikegami, Atsushi Iwasaki, Akira Matsushita, and Kyohei Okumura, Evaluating the Efficiency of Cap-Based Regulation in Matching Markets with Distributional Disparities (New draft: Jan 2, 2025)

  Short Summary

  Cap-based regulations are a practical policy tool for addressing distributional disparities in matching markets. This study develops a theoretical and empirical framework to evaluate the effectiveness of such cap-based regulations by integrating regional constraints into a transferable utility matching model. Using novel data from the Japan Residency Matching Program, we estimate participants’ preferences and simulate the matching outcomes under various policies to evaluate their effectiveness. Our findings reveal that modest monetary incentives and adjustments to regional caps improve the allocation of residents to underserved areas.
  Presentations

  IIOC 2025, APIOC 2024, NYU seminar, JEA annual meeting 2024

• Kei Ikegami, Ken Onishi, and Naoki Wakamori, Joint Venture Formation in Procurement Auctions (New draft: Oct 23, 2024)

  Short Summary

  We propose a model for joint venture formation in the context of procurement auctions. This model enables us to identify the formation mechanism, which is necessary for simulating counterfactual auction settings. We estimate the model using newly collected Japanese procurement auction data. Our estimates reveal the presence of cost synergies: joint ventures are more likely to be cost-effective compared to standard bidders. Despite this pro-competitive effect, our simulation indicates that excessive encouragement of joint ventures hinders cost-effective procurement by reducing competition. This anti-competitive effect arises from the diminished incentive to enter the auction due to the possibility to compete with joint ventures.
  Presentations

  AEA 2024, Otaru University of Commerce, Yokohama National University, NYU seminar, APIOC 2022

• Kei Ikegami, Resource Procurement for Matching Market: A Nash-in-Nash Approach

  Short Summary

  This paper examines the procurement of resources for a subsequent matching market. We present a three-stage model: 1) bilateral bargaining between procurers and resource suppliers, 2) suppliers' decisions on resource provision, and 3) the realization of a stable matching outcome. We adopt the Nash-in-Nash approach as the solution concept for bargaining, revealing a unique equilibrium where procurers are unable to incentivize suppliers, resulting in minimal procurement. However, we demonstrate that by committing to an assignment rule that reverses the order of assignment, the government can increase the number of procured resources in equilibrium. Our findings emphasize the social benefits of integrating the allocation and procurement problems.

• Kei Ikegami and Hikaru Kawarazaki, Social Learning in Budget Formulation: A Case of Adaptation to Natural Disasters

  Short Summary

  This paper studies social learning among policymakers when formulating a budget. Focusing on the disaster prevention policy, we model local governments’ expenditures as a response to the expected future disaster risk. Through this model, we associate the correlation of the expenditures between local governments with the connection in the social learning about the risk. We use Japanese administrative data over 20 years to estimate a sparse social learning network. Moreover, as the network formation determinants, we find significant effects of (1) the inflow of internal migration between local governments, (2) the risk of future earthquakes, and (3) the risk preference of the local citizens.
  Presentations

  KCL, UCL, IFS, GRIP, AASLE Annual Conference at the University of Tokyo, and the Applied Econometric Conference at Waseda University

Work in Progress

• Kei Ikegami and Kan Kuno, Wage Stagnation in Daycare Industry: A Two-Sided Market Perspective