Top Trading Cycles Research Articles

Strategy-proof and nonbossy allocation of indivisible goods and money

Which strategy-proof nonbossy mechanisms exist in a model with a finite number of indivisible goods (houses, jobs, positions) and a perfectly divisible good (money)? The main finding is that only a finite number of distributions of the divisible good is consistent with strategy-proofness and nonbossiness. Under various additional assumptions - neutrality, individual rationality, object efficiency, weak decentralization - the distribution of the divisible good is further restricted. For instance, under neutrality the outcome of the mechanism can have only one distribution, which is hence independent of individual preferences. In this case the mechanism becomes serially dictatorial. On the other hand, individual rationality leads to a fixed price equilibrium with a well-defined rationing method (Gale's top-trading cycle procedure).

House Allocation with Existing Tenants: An Equivalence

In this paper we analyze two house allocation mechanisms each of which is designed to eliminate inefficiencies in real-life house allocation problems where there are both existing tenants and newcomers. The first mechanism chooses the unique core allocation of a sister exchange economy which is constructed by assigning each existing tenant her current house and randomly assigning each newcomer a vacant house. The second mechanism -top trading cycles mechanism- first chooses an ordering from a given distribution and next determines the final outcome as follows: Assign first agent her top choice, next agent her top choice among remaining houses and so on, until someone demands house of an existing tenant who is still in the line. At that point modify the queue by inserting her at the top and proceed. Similarly, insert any existing tenant who is not already served at the top of the queue once her house is demanded. Whenever a loop of existing tenants forms, assign each of them the house she demands and proceed. Our main result is that the core based mechanism is equivalent to an extreme case of the top trading cycles mechanism which orders newcomers before the existing tenants.

Strategyproof Assignment by Hierarchical Exchange

We give a characterization of the set of group-strategyproof, Pareto-optimal, and reallocation-proof allocation rules for the assignment problem, where individuals are assigned at most one indivisible object, without any medium of exchange. Although there are no property rights in the model, the rules satisfying the above criteria imitate a trading procedure with individual endowments, in which individuals exchange objects from their hierarchically determined endowment sets in an iterative manner. In particular, these assignment rules generalize Gale's top trading cycle procedure, the classical rule for the model in which each individual owns an indivisible good.

Group incentive compatibility in a market with indivisible goods

In a market where each trader has one unit of an indivisible good, there are procedures for exchanging goods which result in competitive allocations. One of these procedures, the top trading cycle, has the property that it is in each trader's best interest to report his true preferences over the set of goods. This note shows that no subset of traders can misrepresent their preferences and improve the allocation for all members of the subset. Additionally, if there are no indifferences in the preferences, then some traders in a subset that misrepresents preferences do worse.