Core Concepts
The core message of this paper is to provide an axiomatic characterization of allocation mechanisms in decentralized exchange markets with frictional costs, where certain transfers between agents result in costs to the economy. The authors introduce the notion of "frictional participation" to capture these frictions and show how it leads to a representation of allocation mechanisms as robust linear mechanisms or robust conditional mean allocation mechanisms.
Abstract
The paper examines allocation mechanisms in a decentralized pure-exchange economy under uncertainty, where agents have initial state-contingent endowments. The authors argue that certain types of transfers between agents, namely initial transfers of state-contingent endowments to any agent with zero initial endowment, result in costs to the economy, which they call "frictional costs".
The authors introduce the notion of an "allocation mechanism" that transforms feasible allocations of the aggregate endowment into other feasible allocations, and they propose an axiomatic study of such mechanisms in the presence of frictional costs. They introduce several axioms, including Internal Fairness, Agent Anonymity, Operational Anonymity, Frictional Participation, and Scale Invariance.
The authors show that the combination of these axioms characterizes two classes of allocation mechanisms: robust allocation mechanisms and robust conditional mean allocation mechanisms. Robust allocation mechanisms are represented as worst-case linear allocation mechanisms, while robust conditional mean allocation mechanisms are represented as worst-case conditional expectations.
The authors also discuss the relationship between their results and the literature on decentralized risk sharing within a pool of agents, providing an axiomatization of conditional mean allocation mechanisms and a subjective version of the Conditional Mean Risk Sharing (CMRS) rule.
Finally, the authors present two examples of robust allocation mechanisms: the Mean-Deviation allocation mechanism and the Expected-Shortfall allocation mechanism, and analyze the impact of parameters such as correlation and risk attitudes on the global frictional costs and the incentives for agents to participate in the risk-sharing pool.