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Social and Information Sciences Laboratory (SISL) Seminar

Friday, November 8, 2019
12:00pm to 1:00pm
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Baxter 125
What matters in tie-breaking rules? How competition guides design
Afshin Nikzad, Assistant Professor of Economics, Dornsife College of Letters, Arts and Sciences, USC,

Abstract: Many school districts apply the student-proposing deferred acceptance algorithm after ties among students are broken exogenously. We compare two common tie-breaking rules: one in which all schools use a single common lottery, and one in which every school uses a separate independent lottery. We identify the balance between supply and demand as the determining factor in this comparison. First we analyze a two-sided matching model with random preferences in over-demanded and under-demanded markets. In a market with a surplus of seats a common lottery is less equitable and there are efficiency trade-offs between the two tie-breaking rules. However, a common lottery is always preferable when there is shortage of seats. The theory suggests that popular schools should use a common lottery to resolve ties. We run numerical experiments with New York City choice data after partitioning the market into popular and non-popular schools. The experiments support our findings.

For more information, please contact Mary Martin by phone at 626-395-4571 or by email at