College admissions with affirmative action

This paper first shows that when colleges' preferences are substitutable there does not exist any stable matching mechanism that makes truthful revelation of preferences a dominant strategy for every student. The paper introduces student types and captures colleges' preferences for affirmative action via type-specific quotas: A college always prefers a set of students that respects its type-specific quotas to another set that violates them. Then it shows that the student-applying deferred acceptance mechanism makes truthful revelation of preferences a dominant strategy for every student if each college's preferences satisfy responsiveness over acceptable sets of students that respect its type-specific quotas. These results have direct policy implications in several entry-level labor markets (Roth 1991). Furthermore, a fairness notion and the related incentive theory developed here is applied to controlled choice in the context of public school choice by Abdulkadiroglu and Sönmez (2003)

Trust, reciprocity and favors in cooperative relationships

We study trust, reciprocity and favors in a repeated trust game with private information. In our main analysis, players are willing to exhibit trust and thereby facilitate cooperative gains only if such behavior is regarded as a favor that must be reciprocated, either immediately or in the future. Private information is a fundamental ingredient in our theory. A player with the ability to provide a favor must have the incentive to reveal this capability, and this incentive is provided by an equilibrium construction in which favors are reciprocated. We also offer the novel prediction that the size of a favor owed may decline over time, as neutral phases of the relationship are experienced. Indeed, a favor-exchange relationship with this feature offers a higher total payoff than does a simple favor-exchange relationship. We also describe specific circumstances in which a relationship founded on favor exchange may be inferior to a relationship in which an infrequent and symmetric punishment motivates cooperative behavior. Finally, we show that a hybrid relationship, in which players begin with a honeymoon period and then either proceed to a favor-exchange relationship of suffer a symmetric punishment, can also offer scope for improvement

Mechanism design with tacit collusion

In the mechanism design literature, collusion is often modelled as agents signing side contracts. This modelling approach is in turn implicitly justified by some unspecified repeated-interaction story. In this paper, we first second-guess what kind of repeated-interaction story these side-contract theorists (would admit that they) are having in mind. We then show that, within this repeated-interaction story, there is a big difference between communicative and tacit collusion. While communicative collusion hurts the mechanism designer, tacit collusion is exploitable

Room Assignment-Rent Division: A Market Approach

A 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.

Unemployment insurance and the role of self-insurance

This paper employs a dynamic general equilibrium model to design and evaluate long-term unemployment insurance plans (plans that depend on workers' unemployment history) in economies with and without hidden savings. We show that optimal benefit schemes and welfare implications differ considerably in these two economies. Switching to long-term plans can improve welfare significantly in the absence of hidden savings. However, welfare gains are much lower when we consider hidden savings. Therefore, we argue that switching to long-term plans should not be a primary concern from a policy point of view

Changing the Boston School Choice Mechanism

In July 2005 the Boston School Committee voted to replace the existing Boston school choice mechanism with a deferred acceptance mechanism that simplifies the strategic choices facing parents. This paper presents the empirical case against the previous Boston mechanism, a priority matching mechanism, and the case in favor of the change to a strategy-proof mechanism. Using detailed records on student choices and assignments, we present evidence both of sophisticated strategic behavior among some parents, and of unsophisticated strategic behavior by others. We find evidence that some parents pay close attention to the capacity constraints of different schools, while others appear not to. In particular, we show that many unassigned students could have been assigned to one of their stated choices with a different strategy under the current mechanism. This interaction between sophisticated and unsophisticated players identifies a new rationale for strategy-proof mechanisms based on fairness, and was a critical argument in Boston's decision to change the mechanism. We then discuss the considerations that led to the adoption of a deferred acceptance mechanism as opposed to the (also strategy-proof) top trading cycles mechanism.

Resolving Conflicting Preferences in School Choice

The Boston mechanism is among the most popular school choice procedures in use. Yet, the mechanism has been criticized for its poor incentive and welfare performances, which led the Boston Public Schools to recently replace it with Gale and Shapley's deferred acceptance algorithm (henceforth, DA). The DA elicits truthful revelation of "ordinal" preferences whereas the Boston mechanism does not; but the latter induces participants to reveal their "cardinal" preferences (i.e., their relative preference intensities) whereas the former does not. We show that cardinal preferences matter more when families have similar ordinal preferences and schools have coarse priorities, two common features of many school choice environments. Specifically, when students have the same ordinal preferences and schools have no priorities, the Boston mechanism Pareto dominates the DA in ex ante welfare. The Boston mechanism may not harm but rather benefit participants who may not strategize well. In the presence of school priorities, the Boston mechanism also tends to facilitate a greater access than the DA to good schools by those lacking priorities at those schools. These results contrast with the standard view, and cautions against a hasty rejection of the Boston mechanism in favor of mechanisms such as the DA

The New York City High School Match

Economic