Justified representation in approval-based committee voting
We consider approval-based committee voting, i.e. the setting where each voter approves a subset of candidates, and these votes are then used to select a fixed-size set of winners (committee). We propose a natural axiom for this setting, which we call justified representation (JR). This axiom requir...
| Main Authors: | , , , , , |
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| Format: | Journal article |
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Springer Verlag
2017
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| _version_ | 1826295489620869120 |
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| author | Aziz, H Brill, M Conitzer, V Elkind, E Freeman, R Walsh, T |
| author_facet | Aziz, H Brill, M Conitzer, V Elkind, E Freeman, R Walsh, T |
| author_sort | Aziz, H |
| collection | OXFORD |
| description | We consider approval-based committee voting, i.e. the setting where each voter approves a subset of candidates, and these votes are then used to select a fixed-size set of winners (committee). We propose a natural axiom for this setting, which we call justified representation (JR). This axiom requires that if a large enough group of voters exhibits agreement by supporting the same candidate, then at least one voter in this group has an approved candidate in the winning committee. We show that for every list of ballots it is possible to select a committee that provides JR. However, it turns out that several prominent approval-based voting rules may fail to output such a committee. In particular, while Proportional Approval Voting (PAV) always outputs a committee that provides JR , Sequential Proportional Approval Voting (SeqPAV), which is a tractable approximation to PAVP, does not have this property. We then introduce a stronger version of the JR axiom, which we call extended justified representation (EJR), and show that PAV satisfies EJR, while other rules we consider do not; indeed, EJR can be used to characterize PAV within the class of weighted PAV rules. We also consider several other questions related to JR and EJR, including the relationship between JR/EJR and core stability, and the complexity of the associated computational problems. |
| first_indexed | 2024-03-07T04:01:52Z |
| format | Journal article |
| id | oxford-uuid:c4d31e50-4dde-4568-bd12-4603f26f7d2f |
| institution | University of Oxford |
| last_indexed | 2024-03-07T04:01:52Z |
| publishDate | 2017 |
| publisher | Springer Verlag |
| record_format | dspace |
| spelling | oxford-uuid:c4d31e50-4dde-4568-bd12-4603f26f7d2f2022-03-27T06:26:41ZJustified representation in approval-based committee votingJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:c4d31e50-4dde-4568-bd12-4603f26f7d2fSymplectic Elements at OxfordSpringer Verlag2017Aziz, HBrill, MConitzer, VElkind, EFreeman, RWalsh, TWe consider approval-based committee voting, i.e. the setting where each voter approves a subset of candidates, and these votes are then used to select a fixed-size set of winners (committee). We propose a natural axiom for this setting, which we call justified representation (JR). This axiom requires that if a large enough group of voters exhibits agreement by supporting the same candidate, then at least one voter in this group has an approved candidate in the winning committee. We show that for every list of ballots it is possible to select a committee that provides JR. However, it turns out that several prominent approval-based voting rules may fail to output such a committee. In particular, while Proportional Approval Voting (PAV) always outputs a committee that provides JR , Sequential Proportional Approval Voting (SeqPAV), which is a tractable approximation to PAVP, does not have this property. We then introduce a stronger version of the JR axiom, which we call extended justified representation (EJR), and show that PAV satisfies EJR, while other rules we consider do not; indeed, EJR can be used to characterize PAV within the class of weighted PAV rules. We also consider several other questions related to JR and EJR, including the relationship between JR/EJR and core stability, and the complexity of the associated computational problems. |
| spellingShingle | Aziz, H Brill, M Conitzer, V Elkind, E Freeman, R Walsh, T Justified representation in approval-based committee voting |
| title | Justified representation in approval-based committee voting |
| title_full | Justified representation in approval-based committee voting |
| title_fullStr | Justified representation in approval-based committee voting |
| title_full_unstemmed | Justified representation in approval-based committee voting |
| title_short | Justified representation in approval-based committee voting |
| title_sort | justified representation in approval based committee voting |
| work_keys_str_mv | AT azizh justifiedrepresentationinapprovalbasedcommitteevoting AT brillm justifiedrepresentationinapprovalbasedcommitteevoting AT conitzerv justifiedrepresentationinapprovalbasedcommitteevoting AT elkinde justifiedrepresentationinapprovalbasedcommitteevoting AT freemanr justifiedrepresentationinapprovalbasedcommitteevoting AT walsht justifiedrepresentationinapprovalbasedcommitteevoting |