Researcher: Sönmez, Tayfun
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Sönmez, Tayfun
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Publication Metadata only Ordinal efficiency and dominated sets of assignments(Academic Press Inc Elsevier Science, 2003) Abdülkadiroğlu, Atila; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AUsing lotteries is a common tool for allocating indivisible goods. Since obtaining preferences over lotteries is often difficult, real-life mechanisms usually rely on ordinal preferences over deterministic outcomes. Bogomolnaia and Moulin (J. Econom. Theory 19 (2002) 623) show that the outcome of an ex post efficient mechanism may be stochastically dominated They define a random assignment to be ordinally efficient if and only if it is not stochastically dominated. In this paper we investigate the relation between ex post efficiency and ordinal efficiency. We introduce a new notion of domination defined over sets of assignments and show that a lottery induces an ordinally efficient random assignment if and only if each subset of the full support of the lottery is undominated.Publication Metadata only Kidney exchange(Massachusetts Institute of Technology (MIT) Press, 2004) Roth, Alvin E.; Department of Economics; Department of Economics; Department of Economics; Sönmez, Tayfun; Ünver, Utku; Faculty Member; Faculty Member; College of Administrative Sciences and Economics; College of Administrative Sciences and Economics; N/A; N/AMost transplanted kidneys are from cadavers, but there are also many transplants from live donors. Recently, there have started to be kidney exchanges involving two donor-patient pairs such that each donor cannot give a kidney to the intended recipient because of immunological incompatibility, but each patient can receive a kidney from the other donor. Exchanges are also made in which a donor-patient pair makes a donation to someone waiting for a cadaver kidney, in return for the patient in the pair receiving high priority for a compatible cadaver kidney when one becomes available. There are stringent legal/ethical constraints on how exchanges can be conducted. We explore how larger scale exchanges of these kinds can be arranged efficiently and incentive compatibly, within existing constraints. The problem resembles some of the "housing" problems studied in the mechanism design literature for indivisible goods, with the novel feature that while live donor kidneys can be assigned simultaneously, cadaver kidneys cannot. In addition to studying the theoretical properties of the proposed kidney exchange, we present simulation results suggesting that the welfare gains from larger scale exchange would be substantial, both in increased number of feasible live donation transplants, and in improved match quality of transplanted kidneys.Publication Metadata only House allocation with existing tenants(Academic Press Inc, 1999) Abdülkadiroğlu, Atila; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AIn many real-life applications of house allocation problems, whenever an existing tenant wants to move, he needs to give up his current house before getting another one. This practice discourages existing tenants from such attempts and results in loss of potentially large gains from trade. Motivated by this observation, we propose a simple mechanism that is Pareto efficient, individually rational, and strategy-proof. Our approach is constructive and we provide two algorithms, each of which can be used to find the outcome of this mechanism. One additional merit of this mechanism is that it can accommodate any hierarchy of seniorities.Publication Metadata only An experimental study of house allocation mechanisms(Elsevier Science Sa, 2004) Chen, Yan; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AWe report an experiment on three house allocation mechanisms under complete information: random serial dictatorship with squatting rights, and two variants of the top trading cycles mechanism. Results show that the latter two are significantly more efficient than the former.Publication Metadata only School choice: an experimental study(Academic Press Inc Elsevier Science, 2006) Chen, Yan; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AWe present an experimental study of three school choice mechanisms. The Boston mechanism is influential in practice, while the Gale-Shapley and Top Trading Cycles mechanisms have superior theoretical properties. Consistent with theory, this study indicates a high preference manipulation rate under Boston. As a result, efficiency under Boston is significantly lower than that of the two competing mechanisms in the designed environment. However, contrary to theory, Gale-Shapley outperforms Top Trading Cycles and generates the highest efficiency. Our results suggest that replacing the Boston mechanism with either Gale-Shapley or Top Trading Cycles mechanism might significantly improve efficiency.Publication Metadata only Can pre-arranged matches be avoided in two-sided matching markets?(Academic Press Inc, 1999) Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AWe study manipulation via pre-arranged matches in the context of centralized two-sided matching markets. We show that the solution that is used to match the hospitals and medical residents in the United States, namely the hospital-optimal stable rule, is manipulable in this way. Unfortunately this is a general problem: We show that there is no solution that is both stable and non-manipulable.Publication Metadata only Core in a simple coalition formation game(Springer, 2001) Banerjee, Suryapratim; Konishi, Hideo; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AWe analyze the core of a class of coalition formation game in which every player's payoff depends only on the members of her coalition. We first consider anonymous games and additively separable games. Neither of these strong properties guarantee the existence of a core allocation, even if additional strong properties are imposed. We then introduce two top-coalition properties each of which guarantee the existence. We show that these properties are independent of the Scarf-balancedness condition. Finally we give several economic applications.Publication Metadata only Room assignment-rent division: a market approach(Springer, 2004) Abdulkadiroğlu, Atila; Department of Economics; Department of Economics; Department of Economics; Sönmez, Tayfun; Ünver, Utku; Faculty Member; Faculty Member; College of Administrative Sciences and Economics; College of Administrative Sciences and Economics; N/A; N/AA group of friends consider renting a house but they shall first agree on how to allocate its rooms and share the rent. We propose an auction mechanism for room assignment-rent division problems which mimics the market mechanism. Our auction mechanism is efficient, envy-free, individually-rational and it yields a non-negative price to each room whenever that is possible with envy-freeness.Publication Metadata only School choice: a mechanism design approach(American Economic Association (AEA), 2003) Abdulkadiroglu, Atila; Department of Economics; Department of Economics; Sönmez, Tayfun; Faculty Member; College of Administrative Sciences and Economics; N/AA central issue in school choice is the design of a student assignment mechanism. Education literature provides guidance for the design of such mechanisms but does not offer specific mechanisms. The flaws in the existing school choice plans result in appeals by unsatisfied parents. We formulate the school choice problem as a mechanism design problem and analyze some of the existing school choice plans including those in Boston, Columbus, Minneapolis, and Seattle. We show that these existing plans have serious shortcomings, and offer two alternative mechanisms each of which may provide a practical solution to some critical school choice issues.Publication Metadata only House allocation with existing tenants: an equivalence(academic Press inc Elsevier Science, 2005) Department of Economics; Department of Economics; Department of Economics; Sönmez, Tayfun; Ünver, Utku; Faculty Member; Faculty Member; College of Administrative Sciences and Economics; College of Administrative Sciences and Economics; N/A; N/AWe analyze two mechanisms designed to eliminate inefficiencies in house allocation problems where there are both existing tenants and newcomers. the first mechanism chooses the unique core allocation of a "sister" exchange economy constructed by endowing each existing tenant with her current house and each newcomer with a random vacant house. the second mechanism chooses an ordering from a given distribution and determines the final outcome as follows: assign the agents the best available house one-at-a-time following their ordering in the queue and whenever an agent demands the house of an existing tenant who is still in the line, modify the queue by inserting the existing tenant at the top. Whenever a loop of existing tenants forms, Assign each of them the house she demands and proceed. We show that the first mechanism is equivalent to an extreme case of the second which favors the newcomers.