Online Social Choice and Welfare Seminar: Agustín Bonifacio, Tuesday 14 April
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Marcus Pivato
Apr 7, 2026, 4:59:37 PM (13 days ago) Apr 7
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 (14 April). Here are the details.
Time: 2PM GMT (10AM Toronto/Montréal, 11AM San Luis, 3PM London, 4PM Saint Etienne, 5PM Istanbul, 7:30PM New Delhi, 11PM Tokyo/Seoul)
Speaker: Agustín Bonifacio (GATE Saint-Étienne and Instituto de Matemática Aplicada San Luis)
Title: "Obvious Manipulations by Groups"
Abstract. We introduce the notion of obvious manipulation by groups, extending obvious manipulability from individual to coalitional deviations. While existing work focuses on individual incentives, coordinated deviations are often natural, calling for a notion of obviousness at the group level.
We propose a definition based on simple best- and worst-case reasoning and study its implications for voting rules. In tops-only domains, ruling out obvious group manipulations imposes strong restrictions: it implies efficiency, monotonicity, and an almost-unanimity property.
Our main result shows that any tops-only, monotonic voting rule that is not obviously manipulable by groups must be dictatorial. This is somewhat surprising in light of the positive results for individual non-obvious manipulability, where rich classes of rules can be sustained. By contrast, robustness to obvious group deviations sharply limits the design of voting rules.
We also show that many standard rules satisfying the majority criterion are vulnerable to obvious group manipulations. Overall, our results provide a first step toward a theory of group obviousness and uncover new tensions between collective incentives and classical voting principles.
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.
Dear all,
The next presentation in the Online Social Choice and Welfare Seminar will be next Tuesday (14 April). Here are the details.
Time: 2PM GMT (10AM Toronto/Montréal, 11AM San Luis, 3PM London, 4PM Saint Etienne, 5PM Istanbul, 7:30PM New Delhi, 11PM Tokyo/Seoul)
Speaker: Agustín Bonifacio (GATE Saint-Étienne and Instituto de Matemática Aplicada San Luis)
Title: "Obvious Manipulations by Groups"
Abstract. We introduce the notion of obvious manipulation by groups, extending obvious manipulability from individual to coalitional deviations. While existing work focuses on individual incentives, coordinated deviations are often natural, calling for a notion of obviousness at the group level.
We propose a definition based on simple best- and worst-case reasoning and study its implications for voting rules. In tops-only domains, ruling out obvious group manipulations imposes strong restrictions: it implies efficiency, monotonicity, and an almost-unanimity property.
Our main result shows that any tops-only, monotonic voting rule that is not obviously manipulable by groups must be dictatorial. This is somewhat surprising in light of the positive results for individual non-obvious manipulability, where rich classes of rules can be sustained. By contrast, robustness to obvious group deviations sharply limits the design of voting rules.
We also show that many standard rules satisfying the majority criterion are vulnerable to obvious group manipulations. Overall, our results provide a first step toward a theory of group obviousness and uncover new tensions between collective incentives and classical voting principles.
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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