## Publications

**Maricano-Romm, D., Romm, A., Bourgeois Gironde, S., and Deouell, L.,**

**The Alternative Omen Effect: Illusory Negative Correlation Between the Outcomes of Choice Options, Cognition (forthcoming)**

**Frick M., and Romm, A., Rational Behavior under Correlated Uncertainty,**

**Journal of Economic Theory (forthcoming)**

**Click for abstract**

In complete information games, Dekel and Fudenberg (1990) and Börgers (1994) have proposed the solution concept \( S^\infty W \) (one round of elimination of weakly dominated strategies followed by iterated elimination of strongly dominated strategies), motivating it by a characterization in terms of “approximate common knowledge” of admissibility. We examine the validity of this characterization of \( S^\infty W \) in an incomplete information setting. We argue that in Bayesian games with a nontrivial state space, the characterization is very sensitive to the way in which uncertainty in the form of approximate common knowledge of admissibility is taken to interact with the uncertainty already captured by players’ beliefs about the states of nature: We show that \( S^\infty W \) corresponds to approximate common knowledge of admissibility when this is not allowed to coincide with any changes to players’ beliefs about states. If approximate common knowledge of admissibility is accompanied by vanishingly small perturbations to beliefs, then \( S^\infty W \) is a (generally strict) subset of the predicted behavior, which we characterize in terms of a generalization of Hu’s (2007) perfect p-rationalizable set.

**Bronfman S., Hassidim A., Afek A., Romm A., Sherberk R., Hassidim A., and Massler A., Assigning Israeli Medical Graduates to Internships, Israel Journal of Health Policy Research (2015)**

**Click for abstract**

Upon completion of the medical studies, and before getting the diploma, doctors in Israel are required to do an internship in a hospital. For most students, the assignment is determined by a lottery, which takes into consideration the preferences of these students. We propose a novel way to perform this lottery, in which (on average) a larger number of students gets one of their top choices. We report about implementing this method in the 2014 Internship Lottery in Israel.

**Romm A., Implications of Capacity Reduction and Entry in Many-to-One Stable Matching, Social Choice and Welfare (2014) (Accepted manuscript version)**

**Click for abstract**

In two-sided many-to-one matching markets some mechanisms induce worse allocations for one side of the market following a capacity reduction on the other side. This prediction, however, is not true for all matching mechanisms. Assuming preferences are strict and responsive, we are able to provide comparative statistics involving subsets of agents on both sides of the market for all stable mechanisms. Within the larger domain of substitutable preferences capacity reductions may have ambiguous consequences. Nevertheless, if preferences satisfy the law of aggregate demand a similar result does hold. These results are an extension of the one-to-one results on entry of Roth and Sotomayor (1990) to many-to-one environments. Finally, we consider truncation strategies, and describe how agents may manipulate the matching process to their advantage, without knowing which stable mechanism is being used either by reporting a truncated preference or by shading capacity.

**Romm A.,**Solution to Exchanges 8.2 Puzzle: A Dutch Dutch Auction Clock Auction,

**Sigecom Exchanges (2011), 10.1.**

## Working papers

**An Approximate Law of One Price in Random Assignment Markets (**

**with**Avinatan Hassidim

**, preliminary version in EC'15)**

**Click for abstract**

Assignment games represent a tractable model of two-sided markets with transfers. We study the likely properties of the core of randomly generated assignment games. When the joint productivity of every firm and worker has a noise element with a bounded distribution, with high probability all workers who have approximately the same human capital level are paid roughly equal wages, and all firms of similar quality make similar profits. This implies that core allocations vary significantly in balanced markets, but that there is core convergence in even slightly unbalanced markets. The same phenomenon occurs when firms' quality and workers' human capital level are complementary factors in productivity. When the noise element is unbounded, there may be a large variation in payoffs.

**Click for abstract**

We present a bargaining model with incomplete information and players who repeatedly revise their actions over a finite period of time. For an open set of parameters, one-sided reputation-building leads to a deadline effect in the form of last-minute strategic interaction, and is linked with a non-negligible risk of reaching an inefficient outcome. Two-sided reputation-formation necessarily induces substantial delay and inefficiency with positive probability.

**Redesigning the Israeli Medical Internship Match (with Noga Alon, Slava Bronfman and Avinatan Hassidim, preliminary version in EC'15)**

**Click for abstract**

The final step in getting an Israeli M.D. is performing a year-long internship in one of the hospitals in Israel. Internships are decided upon by a lottery, which is known as “The Internship Lottery”. In 2014 we redesigned the lottery, replacing it with a more efficient one. This paper presents the market, the redesign process and the new mechanism which is now in use. There are two main lessons that we have learned from this market. The first is the “Do No Harm” principle, which states that (almost) all participants should prefer the new mechanism to the old one. The second is that new approaches need to be used when dealing with two-body problems in object assignment. We focus on the second lesson, and study two-body problems in the context of the assignment problem. We show that decomposing stochastic assignment matrices to deterministic allocations is NP-hard in the presence of couples, and present a polynomial time algorithm with the optimal worst case guarantee. We also study the performance of our algorithm on real-world and on simulated data.

**Assigning More Students to Their Top Choices: A Tiebreaking Rule Comparison (with Itai Ashlagi and Afshin Nikzad, preliminary version in EC'15)**

**Click for abstract**

School choice districts that implement stable matchings face various design issues that impact students’ assignments to schools. We study properties of the rank distribution of students with random preferences, when schools use different tiebreaking rules to rank equivalent students. We find that under a multiple tiebreaking rule a vanishing fraction of students match to one of their top choices, in contrast to a single tiebreaking rule under which a constant fraction of students are assigned to one of their top choices. We find that when students can submit only a relatively short preference list, the multiple tiebreaking rule allows a constant fraction of students to match to one of their top choices, with only a “small” fraction of students remaining unmatched.

## In progress

**Information Effects of jump Bidding in English Auctions (with Dror Lellouche)**

**Click for abstract**

When there are three players or more with interdependent values and affiliated signals, a bidder may want to jump bid in order to obscure some players' signals from other other opponents. If the jumper's signal is partially revealed in the process, this behavior is not likely to appear in equilibrium, unless there are other factors (e.g. risk aversion) at play.

**Courting and interviewing in Matching Markets (with Avinatan Hassidim)**

**Interviewing in Matching Markets (with Itai Ashlagi, Mark Braverman and Avinatan Hassidim)**

**Waitlists in School Choice (with Itai Ashlagi)**

**"Strategic" Players in a Strategy-Proof Environment (with Avinatan Hassidim, Deborah Marciano-Romm and Ran Shorrer)**

## Software

## Other publications

**On artificially induced inefficiencies in Israeli tax reporting system**

**(In Hebrew, TheMarker, April 2010)**

**Humorous economic analysis of behavior in dating websites**

**(In Hebrew, ynet, December 2009)**