The Art of Two-Round Voting
Qishen Han, Grant Schoenebeck, Biaoshuai Tao, Lirong Xia

TL;DR
This paper demonstrates that two-round voting mechanisms can reliably lead to majority-preferred decisions, are easier to analyze, and outperform one-round voting in AI simulations, offering a practical approach for collective decision-making.
Contribution
It introduces the two-round voting mechanism as a natural, effective alternative to one-round voting, ensuring informed majority decisions and simpler equilibrium analysis.
Findings
Two-round voting aligns with majority preferences.
Equilibria in two-round voting are easier to characterize.
Two-round voting outperforms one-round voting in AI experiments.
Abstract
We study the voting problem with two alternatives where voters' preferences depend on a not-directly-observable state variable. While equilibria in the one-round voting mechanisms lead to a good decision, they are usually hard to compute and follow. We consider the two-round voting mechanism where the first round serves as a polling stage and the winning alternative only depends on the outcome of the second round. We show that the two-round voting mechanism is a powerful tool for making collective decisions. Firstly, every (approximated) equilibrium in the two-round voting mechanisms (asymptotically) leads to the decision preferred by the majority as if the state of the world were revealed to the voters. Moreover, there exist natural equilibria in the two-round game following intuitive behaviors such as informative voting, sincere voting [Austen-Smith and Banks, 1996], and the…
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Taxonomy
TopicsElectoral Systems and Political Participation
