Online Social Choice and Welfare Seminar: Théo Delemazure, Tuesday 18 November
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Marcus Pivato
Nov 11, 2025, 4:31:30 PMNov 11
to social-choice-a...@googlegroups.com, com...@duke.edu
[with apologies for cross-posting]
Dear all,
The next presentation in the Online Social Choice and Welfare Seminar will be next Tuesday (18 November). Here are the details.
Dear all,
The next presentation in the Online Social Choice and Welfare Seminar will be next Tuesday (18 November). Here are the details.
Time:
2PM GMT (9AM Montréal/Toronto, 11AM Rio de Janeiro, 2PM London, 3PM
Amsterdam, 5PM Istanbul, 7:30PM New Delhi, 11PM Tokyo/Seoul)
Speaker: Théo Delemazure (Institute for Logic, Language and Computation)
Title: "Comparing Ways of Obtaining Candidate Axes from Approval Ballots"
Abstract: To understand and summarize approval preferences and other binary evaluation data, it is useful to order the items on an axis which explains the data. In a political election using approval voting, this could be an ideological left-right axis such that each voter approves adjacent candidates, an analogue of single-peakedness. In a perfect axis, every approval set would be an interval, which is usually not possible, and so we need to choose an axis that gets closest to this ideal. The literature has developed algorithms for optimizing several objective functions (e.g., minimize the number of added approvals needed to get a perfect axis), but provides little help with choosing among different objectives. In this paper, we take a social choice approach and compare 5 different axis selection rules axiomatically, by studying the properties they satisfy. We establish some impossibility theorems, and characterize (within the class of scoring rules) the rule that chooses the axes that maximize the number of votes that form intervals, using the axioms of ballot monotonicity and resistance to cloning. Finally, we study the behavior of the rules on data from French election surveys, on the votes of justices of the US Supreme Court, and on synthetic data.
Reminder: On the seminar website you can find the video recordings, slides and supplementary materials for all past presentations, as well as information about future presentations.
Speaker: Théo Delemazure (Institute for Logic, Language and Computation)
Title: "Comparing Ways of Obtaining Candidate Axes from Approval Ballots"
Abstract: To understand and summarize approval preferences and other binary evaluation data, it is useful to order the items on an axis which explains the data. In a political election using approval voting, this could be an ideological left-right axis such that each voter approves adjacent candidates, an analogue of single-peakedness. In a perfect axis, every approval set would be an interval, which is usually not possible, and so we need to choose an axis that gets closest to this ideal. The literature has developed algorithms for optimizing several objective functions (e.g., minimize the number of added approvals needed to get a perfect axis), but provides little help with choosing among different objectives. In this paper, we take a social choice approach and compare 5 different axis selection rules axiomatically, by studying the properties they satisfy. We establish some impossibility theorems, and characterize (within the class of scoring rules) the rule that chooses the axes that maximize the number of votes that form intervals, using the axioms of ballot monotonicity and resistance to cloning. Finally, we study the behavior of the rules on data from French election surveys, on the votes of justices of the US Supreme Court, and on synthetic data.
To obtain the Zoom link, please subscribe to the Seminar Mailing List, or contact one of the organisers.
Reminder: On the seminar website you can find the video recordings, slides and supplementary materials for all past presentations, as well as information about future presentations.
--
Marcus Pivato
Centre d'Économie de la Sorbonne
Centre d'Économie de la Sorbonne
Université Paris 1 Panthéon-Sorbonne
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