Paths to stability for matching markets with couples

We study two-sided matching markets with couples and show that for a natural preference domain for couples, the domain of weakly responsive preferences, stable outcomes can always be reached by means of decentralized decision making. Starting from an arbitrary matching, we construct a path of matchings obtained from ‘satisfying’ blocking coalitions that yields a stable matching. Hence, we establish a generalization of Roth and Vande Vate's [Roth, A.E., Vande Vate, J.H., 1990. Random paths to stability in two-sided matching. Econometrica 58, 1475–1480] result on path convergence to stability for decentralized singles markets.Furthermore, we show that when stable matchings exist, but preferences are not weakly responsive, for some initial matchings there may not exist any path obtained from ‘satisfying’ blocking coalitions that yields a stable matching.     

Two-sided matching with interdependent values

We introduce and study two-sided matching with incomplete information and interdependent valuations on one side of the market. An example of such a setting is a matching market between colleges and students in which colleges receive partially informative signals about students. Stability in such markets depends on the amount of information about matchings available to colleges. When colleges observe the entire matching, a stable matching mechanism does not generally exist. When colleges observe only their own matches, a stable mechanism exists if students have identical preferences over colleges, but may not exist if students have different preferences.     

Stochastic stability for roommate markets

We show that for any roommate market the set of stochastically stable matchings coincides with the set of absorbing matchings. This implies that whenever the core is non-empty (e.g., for marriage markets), a matching is in the core if and only if it is stochastically stable, i.e., stochastic stability is a characteristic of the core. Several solution concepts have been proposed to extend the core to all roommate markets (including those with an empty core). An important implication of our results is that the set of absorbing matchings is the only solution concept that is core consistent and shares the stochastic stability characteristic with the core.     

Matching with preferences over colleagues solves classical matching

In this note, we demonstrate that the problem of “many-to-one matching with (strict) preferences over colleagues” is actually more difficult than the classical many-to-one matching problem, “matching without preferences over colleagues.” We give an explicit reduction of any problem of the latter type to a problem of the former type. This construction leads to the first algorithm which finds all stable matchings in the setting of “matching without preferences over colleagues,” for any set of preferences. Our construction directly extends to generalized matching settings.     

Non-revelation mechanisms in many-to-one markets

In this study we present a simple mechanism in a many-to-one matching market where multiple costless applications are allowed. The mechanism is based on the principles of eligibility and priority and it implements the set of stable matchings in Subgame Perfect Nash Equilibrium. We extend the analysis to a symmetric mechanism where colleges and students interchange their roles. This mechanism also implements the set of stable matchings.     

Hedonic price equilibria, stable matching, and optimal transport: equivalence, topology, and uniqueness

Hedonic pricing with quasi-linear preferences is shown to be equivalent to stable matching with transferable utilities and a participation constraint, and to an optimal transportation (Monge–Kantorovich) linear programming problem. Optimal assignments in the latter correspond to stable matchings, and to hedonic equilibria. These assignments are shown to exist in great generality; their marginal indirect payoffs with respect to agent type are shown to be unique whenever direct payoffs vary smoothly with type. Under a generalized Spence-Mirrlees condition (also known as a twist condition) the assignments are shown to be unique and to be pure, meaning the matching is one-to-one outside a negligible set. For smooth problems set on compact, connected type spaces such as the circle, there is a topological obstruction to purity, but we give a weaker condition still guaranteeing uniqueness of the stable match.     

Credible group stability in many-to-many matching problems

It is known that in two-sided many-to-many matching problems, pairwise-stable matchings may not be immune to group deviations, unlike in many-to-one matching problems (Blair, 1988). In this paper, we show that pairwise stability is equivalent to credible group stability when one side has responsive preferences and the other side has categorywise-responsive preferences. A credibly group-stable matching is immune to any “executable” group deviations with an appropriate definition of executability. Under the same preference restriction, we also show the equivalence between the set of pairwise-stable matchings and the set of matchings generated by coalition-proof Nash equilibria of an appropriately defined strategic-form game.     

On the existence of a strictly strong Nash equilibrium under the student-optimal deferred acceptance algorithm

This study analyzes a preference revelation game in the student-optimal deferred acceptance algorithm in a college admission problem. We assume that each college's true preferences are known publicly, and analyze the strategic behavior of students. We demonstrate the existence of a strictly strong Nash equilibrium in the preference revelation game through a simple algorithm that finds it. Specifically, (i) the equilibrium outcome from our algorithm is the same matching as in the efficiency-adjusted deferred acceptance algorithm and (ii) in a one-to-one matching market, it coincides with the student-optimal von Neumann–Morgenstern (vNM) stable matching. We also show that (i) when a strict core allocation in a housing market derived from a college admission market exists, it can be supported by a strictly strong Nash equilibrium, and (ii) there exists a strictly strong Nash equilibrium under the college-optimal deferred acceptance algorithm if and only if the student-optimal stable matching is Pareto-efficient for students.     

Stable schedule matching under revealed preference

Baiou and Balinski (Math. Oper. Res., 27 (2002) 485) studied schedule matching where one determines the partnerships that form and how much time they spend together, under the assumption that each agent has a ranking on all potential partners. Here we study schedule matching under more general preferences that extend the substitutable preferences in Roth (Econometrica 52 (1984) 47) by an extension of the revealed preference approach in Alkan (Econom. Theory 19 (2002) 737). We give a generalization of the Gale-Shapley algorithm and show that some familiar properties of ordinary stable matchings continue to hold. Our main result is that, when preferences satisfy an additional property called size monotonicity, stable matchings are a lattice under the joint preferences of all agents on each side and have other interesting structural properties.     

The welfare effects of pre-arrangements in matching markets

We study the welfare effects of different types of pre-arrangements (as identified in Sönmez in J Econ Theory 86:148–156, 1999) under the intern-optimal and hospital-optimal stable mechanisms in matching markets. First, both mechanisms are manipulable via Type-2 pre-arrangements. Regarding the welfare consequences, they might cause inefficient outcomes to arise, and the welfare effects on each side are ambiguous in the sense that there might be agents from each side, apart from pre-arranging ones, being better and worse off. Then, for Type-1 pre-arrangements, due to Kojima and Pathak (Am Econ Rev 99(3):608–627, 2009), we know that the intern-optimal stable mechanism is immune to this type of manipulations. In contrast to this result, the hospital-optimal stable mechanism turns out to be manipulable. More interestingly, they do not result in inefficient outcomes, and the welfare effects on each side are unambiguous: All hospitals (interns) are better (worse) off.     

Incentives in decentralized random matching markets

Decentralized markets are modeled by means of a sequential game where, starting from any matching situation, firms are randomly given the opportunity to make job offers. In this random context, we prove the existence of ordinal subgame perfect equilibria where firms act according to a list of preferences. Moreover, every such equilibrium preserves stability for a particular profile of preferences. In particular, when firms best reply by acting truthfully, every equilibrium outcome is stable for the true preferences. Conversely, when the initial matching is the empty matching, every stable matching can be reached as the outcome of an ordinal equilibrium play of the game.     

Incomplete information and singleton cores in matching markets

We study ordinal Bayesian Nash equilibria of stable mechanisms in centralized matching markets under incomplete information. We show that truth-telling is an ordinal Bayesian Nash equilibrium of the revelation game induced by a common belief and a stable mechanism if and only if all the profiles in the support of the common belief have singleton cores. Our result matches the observations of Roth and Peranson [The redesign of the matching market for American physicians: some engineering aspects of economic design, Amer. Econ. Rev. 89 (1999) 748-780] in the National Resident Matching Program (NRMP) in the United States: (i) the cores of the profiles submitted to the clearinghouse are small and (ii) while truth-telling is not a dominant strategy most participants in the NRMP truthfully reveal their preferences.     

Von Neumann-Morgenstern stable sets in matching problems

The following properties of the core of a one-to-one matching problem are well-known: (i) the core is non-empty; (ii) the core is a distributive lattice; and (iii) the set of unmatched agents is the same for any two matchings belonging to the core. The literature on two-sided matching focuses almost exclusively on the core and studies extensively its properties. Our main result is the following characterization of (Von Neumann-Morgenstern) stable sets in one-to-one matching problems. We show that a set V of matchings is a stable set of a one-to-one matching problem only if V is a maximal set satisfying the following properties: (a) the core is a subset of V; (b) V is a distributive lattice; and (c) the set of unmatched agents is the same for all matchings belonging to V. Furthermore, a set is a stable set if it is the unique maximal set satisfying properties (a), (b), and (c).     

Holdup, search, and inefficiency

This paper investigates the holdup problem in the search market environment where players search for their trading partners and specific investments are made after matching but before trade decisions are taken. We show that markets with small frictions make the holdup problem more serious than those with large frictions because in any equilibrium, whether stationary or nonstationary, investment must reach the minimum level and trade must be delayed with positive probability for infinitely many time periods. We then show that the gap between equilibrium welfare and the first best welfare becomes larger as search frictions become smaller.     

Absorbing sets in roommate problems

We analyze absorbing sets as a solution for roommate problems with strict preferences. This solution provides the set of stable matchings when it is non-empty and some matchings with interesting properties otherwise. In particular, all matchings in an absorbing set have the greatest number of agents with no incentive to change partners. These “satisfied” agents are paired in the same stable manner. In the case of multiple absorbing sets we find that any two such sets differ only in how satisfied agents are matched with each other.     

Weak stability and a bargaining set for the marriage model

In this note we introduce weak stability, a relaxation of the concept of stability for the marriage model by assuming that the agents are no longer myopic in choosing a blocking pair. The new concept is based on threats within blocking pairs: an individually rational matching is weakly stable if for every blocking pair one of the members can find a more attractive partner with whom he forms another blocking pair for the original matching. Our main result is that under the assumption of strict preferences, the set of weakly stable and weakly efficient matchings coincides with the bargaining set of Zhou (1994, Games Econ. Behav. 6, 512–526) for this context.     

A class of multipartner matching markets with a strong lattice structure

Summary. For a two-sided multipartner matching model where agents are given by path-independent choice functions and no quota restrictions, Blair [7] had shown that stable matchings always exist and form a lattice. However, the lattice operations were not simple and not distributive. Recently Alkan [3] showed that if one introduces quotas together with a monotonicity condition then the set of stable matchings is a distributive lattice under a natural definition of supremum and infimum for matchings. In this study we show that the quota restriction can be removed and replaced by a more general condition named cardinal monotonicity and all the structural properties derived in [3] still hold. In particular, although there are no exogenous quotas in the model there is endogenously a sort of quota; more precisely, each agent has the same number of partners in every stable matching. Stable matchings also have the polarity property (supremum with respect to one side is identical to infimum with respect to the other side) and a property we call {\it complementarity}. Received: May 5, 2000; revised version: January 25, 2001     

The college admissions problem is not equivalent to the marriage problem

Two-sided matching markets of the kind known as the “college admissions problem” have been widely thought to be virtually equivalent to the simpler “marriage problem” for which some striking results concerning agents' preferences and incentives have been recently obtained. It is shown here that some of these results do not generalize to the college admissions problem, contrary to a number of assertions in the recent literature. No stable matching procedure exists that makes it a dominant strategy for colleges to reveal their true preferences, and some outcomes may be preferred by all colleges to the college-optimal stable outcome.     

Incentives in two-sided matching with random stable mechanisms

Summary This paper considers the incentives confronting agents who face the prospect of being matched by some sort of random stable mechanism, such as that discussed in Roth and Vande Vate (1990). A one period game is studied in which all stable matchings can be achieved as equilibria in a natural class of undominated strategies, and in which certain unstable matchings can also arise in this way. A multi-period extension of this game is then considered in which all subgame perfect equilibria must result in stable matchings. These results suggest avenues to explore markets in which matching is organized in a decentralized way.     

Evolutionary choice of markets

We consider an economy where a finite set of agents can trade on one of two asset markets. Due to endogenous participation the markets may differ in the liquidity they provide. Traders have idiosyncratic preferences for the markets, e.g.due to differential time preferences for maturity dates of futures contracts. For a broad range of parameters we find that no trade, trade on both markets (individualization) as well as trade on one market only (standardization) is supported by a Nash equilibrium. By contrast, whenever the number of traders becomes large, the evolutionary process selects a unique stochastically stable state which corresponds to the equilibrium with two active markets and coincides with the welfare maximizing market structure. We are grateful to Thorsten Hens, Fernando Vega-Redondo and a referee for valuable comments. We also thank seminar participants at the University of Zurich, the CES research seminar at the University of Munich, the Koc University in Istanbul as well as conference participants at the SAET conference in Ischia, the ESEM in Lausanne and the ESF workshop on Behavioural Models in Economics and Finance in Vienna. A first version of the paper was written while Marc Oliver Bettzüge was visiting the Institute for Empirical Research in Economics at the University of Zurich. Financial Support by the Swiss Banking Institute and by the National Centre of Competence in Research “Financial Valuation and Risk Management” (NCCR FINRISK) is gratefully acknowledged. The NCCR FINRISK is a research program supported by the Swiss National Science Foundation.