Comment on 'What's the Matter with Tie-Breaking: Improving Efficiency in School Choice'

TL;DR

This paper identifies and corrects a bug in the code used in Erdil & Ergin (2008), clarifying the impact on their computational results while confirming the robustness of their theoretical findings.

Contribution

It provides a corrected implementation of the code used in Erdil & Ergin (2008) and analyzes how the bug affected their empirical results.

Findings

Corrected code reduces the fraction of improving students

Average improvement in rank is larger after correction

Theoretical results remain unchanged

Abstract

The code that was used in Erdil & Ergin (2008, AER) to compute stable improvement cycles sometimes generated unstable matchings. I identify the minor bug in their code that caused this issue, and I present a corrected implementation. While the general insights from the computational experiments obtained by Erdil & Ergin (2008) persist, the true fraction of improving students is slightly smaller than reported, while their average improvement in rank is larger than reported. All theoretical findings in Erdil & Ergin (2008) are unaffected.