The Case for Multiple Tie-Breaking Rules

Speaker: Sumeyra Akin. Assistant Professor at the Economics department of the Pontificia Universidad Católica de Chile (PUC). https://www.sumeyra-akin.com/

Abstract: Centralized school assignment systems typically rely on the deferred acceptance mechanism, where coarse school priorities necessitate tie-breaking rules. Two prominent approaches are the single tie-breaking rule (STB), which uses a single lottery across all schools, and the multiple tie-breaking rule (MTB), which assigns independent lotteries to each school. While STB can yield more top-choice assignments, it also exposes students to extreme luck-based outcomes. In contrast, MTB distributes these risks more evenly, but at the cost of fewer first-choice matches. This paper develops a finite matching model with aligned student preferences to provide a theoretical perspective on policymakers’ preference for MTB. We show that the distribution of rejections under MTB is both lower and less dispersed than under STB, a property that makes MTB more attractive to a risk-averse planner. Our results complement existing empirical and theoretical findings by clarifying when and why MTB may be the more equitable choice in school assignment design.