{"type":"ScholarlyArticle","title":"On Coalitional Manipulation for Multiwinner Elections: Shortlisting","authors":[{"name":"Robert Bredereck","slug":"robert-bredereck","given":"Robert","family":"Bredereck","affiliation":"University of Oxford , United Kingdom ;; TU Berlin , Germany"},{"name":"Andrzej Kaczmarczyk","slug":"andrzej-kaczmarczyk","given":"Andrzej","family":"Kaczmarczyk","affiliation":"TU Berlin , Germany"},{"name":"Rolf Niedermeier","slug":"rolf-niedermeier","given":"Rolf","family":"Niedermeier","affiliation":"TU Berlin , Germany"}],"abstract":"Shortlisting of candidates—selecting a group of “best” candidates—is a special case of multiwinner elections. We provide the first in-depth study of the computational complexity of strategic voting for shortlisting based on the most natural and simple voting rule in this scenario, l-Bloc (every voter approves l candidates). In particular, we investigate the influence of several tie-breaking mechanisms (e.g. pessimistic versus optimistic) and group evaluation functions (e.g. egalitarian versus utilitarian) and conclude that in an egalitarian setting strategic voting may indeed be computationally intractable regardless of the tie-breaking rule. We provide a fairly comprehensive picture of the computational complexity landscape of this neglected scenario.","doi":"10.24963/ijcai.2017/123","url":"https://ijcai.org/proceedings/2017/123","pdf":"https://ijcai.org/proceedings/2017/0123.pdf","markdown":"https://ijcai.org/proceedings/2017/123.md","bibtex":"https://ijcai.org/proceedings/2017/bibtex/123","volume":{"slug":"2017","title":"Proceedings of the Twenty-Sixth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2017","url":"https://ijcai.org/proceedings/2017/","year":2017,"location":"Melbourne, Australia","dates":"19-25 August 2017","editors":"Carles Sierra","isbn":"978-0-9992411-0-3","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2017"},"section":"Knowledge Representation, Reasoning, and Logic","track":"Main track","number":123,"pages":{"first":887,"last":893},"keywords":["Agent-based and Multi-agent Systems: Social Choice Theory","Knowledge Representation, Reasoning, and Logic: Preference modelling and preference-based reasoning"],"videos":[],"references":[{"position":1,"raw":"[Aziz et al., 2015] Haris Aziz, Serge Gaspers, Joachim Gud- mundsson, Simon Mackenzie, Nicholas Mattei, and Toby Walsh. 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