Working Paper: CEPR ID: DP10908
Authors: Alessandra Casella; Thomas Palfrey
Abstract: Vote-trading is common practice in committees and group decision-making. Yet we know very little about its properties. Inspired by the similarity between the logic of sequential rounds of pairwise vote-trading and matching algorithms, we explore three central questions that have parallels in the matching literature: (1) Does a stable allocation of votes always exists? (2) Is it reachable through a decentralized algorithm? (3) What welfare properties does it possess? We prove that a stable allocation exists and is always reached in a finite number of trades, for any number of voters and issues, for any separable preferences, and for any rule on how trades are prioritized. Its welfare properties however are guaranteed to be desirable only under specific conditions. A laboratory experiment confirms that stability has predictive power on the vote allocation achieved via sequential pairwise trades, but lends only weak support to the dynamic algorithm itself.
Keywords: algorithms; matching; vote trading; voting
JEL Codes: C92; D7; D72; P16
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| pivot algorithm (C69) | stable allocation of votes (D72) |
| pivot algorithm (C69) | stability of vote allocations (D72) |
| welfare properties of stable allocations (D69) | conditions of preferences and trade rules (F14) |
| stable allocation of votes (D72) | final vote allocations (D72) |