Sincere favorite criterion

The sincere favorite or no favorite-betrayal criterion is a property of some voting systems, that says voters should have no incentive to vote for someone else over their favorite.^[1] It protects voters from having to engage in a kind of strategy called lesser evil voting or decapitation (i.e. removing the "head" off a ballot).^[2]

Most rated voting systems, including score voting, satisfy the criterion.^[3]^[4]^[5] By contrast, instant-runoff, traditional runoffs, plurality, and most other variants of ranked-choice voting (including all strictly-Condorcet-compliant methods) fail this criterion.^[4]^[6]^[7]

Duverger's law says that systems vulnerable to this strategy will typically (though not always) develop two party-systems, as voters will abandon minor-party candidates to support stronger major-party candidates.^[8]

Instant-runoff voting fails the favorite-betrayal criterion whenever it fails to elect the Condorcet winner, a situation referred to as center-squeeze.

^ Alex Small, “Geometric construction of voting methods that protect voters’ first choices,” arXiv:1008.4331 (August 22, 2010), http://arxiv.org/abs/1008.4331.
^ Merrill, Samuel; Nagel, Jack (1987-06-01). "The Effect of Approval Balloting on Strategic Voting under Alternative Decision Rules". American Political Science Review. 81 (2): 509–524. doi:10.2307/1961964. ISSN 0003-0554. JSTOR 1961964.
^ Baujard, Antoinette; Gavrel, Frédéric; Igersheim, Herrade; Laslier, Jean-François; Lebon, Isabelle (September 2017). "How voters use grade scales in evaluative voting" (PDF). European Journal of Political Economy. 55: 14–28. doi:10.1016/j.ejpoleco.2017.09.006. ISSN 0176-2680. A key feature of evaluative voting is a form of independence: the voter can evaluate all the candidates in turn ... another feature of evaluative voting ... is that voters can express some degree of preference.
^ ^a ^b Wolk, Sara; Quinn, Jameson; Ogren, Marcus (2023-03-20). "STAR Voting, equality of voice, and voter satisfaction: considerations for voting method reform". Constitutional Political Economy (Journal Article). 34 (3): 310–334. doi:10.1007/s10602-022-09389-3. Retrieved 2023-07-16.
^ Eberhard, Kristin (2017-05-09). "Glossary of Methods for Electing Executive Officers". Sightline Institute. Retrieved 2023-12-31.
^ Woodall, Douglas (1997-06-27). "Monotonicity of single-seat preferential election rules". Discrete Applied Mathematics. 77 (1): 81–98. doi:10.1016/S0166-218X(96)00100-X. Retrieved 2024-05-02.
^ Fishburn, Peter; Brams, Steven (1983-09-01). "Paradoxes of Preferential Voting". Mathematics Magazine. 56 (4): 207–214. doi:10.1080/0025570X.1983.11977044. JSTOR 2689808. Retrieved 2024-05-02.
^ Volić, Ismar (2024-04-02). "Duverger's law". Making Democracy Count. Princeton University Press. Ch. 2. doi:10.2307/jj.7492228. ISBN 978-0-691-24882-0.

[small-1] Alex Small, “Geometric construction of voting methods that protect voters’ first choices,” arXiv:1008.4331 (August 22, 2010), http://arxiv.org/abs/1008.4331.

[2] Merrill, Samuel; Nagel, Jack (1987-06-01). "The Effect of Approval Balloting on Strategic Voting under Alternative Decision Rules". American Political Science Review. 81 (2): 509–524. doi:10.2307/1961964. ISSN 0003-0554. JSTOR 1961964.

[3] Baujard, Antoinette; Gavrel, Frédéric; Igersheim, Herrade; Laslier, Jean-François; Lebon, Isabelle (September 2017). "How voters use grade scales in evaluative voting" (PDF). European Journal of Political Economy. 55: 14–28. doi:10.1016/j.ejpoleco.2017.09.006. ISSN 0176-2680. A key feature of evaluative voting is a form of independence: the voter can evaluate all the candidates in turn ... another feature of evaluative voting ... is that voters can express some degree of preference.

[STAR_Analysis-4] Wolk, Sara; Quinn, Jameson; Ogren, Marcus (2023-03-20). "STAR Voting, equality of voice, and voter satisfaction: considerations for voting method reform". Constitutional Political Economy (Journal Article). 34 (3): 310–334. doi:10.1007/s10602-022-09389-3. Retrieved 2023-07-16.

[Sightline-5] Eberhard, Kristin (2017-05-09). "Glossary of Methods for Electing Executive Officers". Sightline Institute. Retrieved 2023-12-31.

[Woodall_Monotonicity-6] Woodall, Douglas (1997-06-27). "Monotonicity of single-seat preferential election rules". Discrete Applied Mathematics. 77 (1): 81–98. doi:10.1016/S0166-218X(96)00100-X. Retrieved 2024-05-02.

[Fishburn-7] Fishburn, Peter; Brams, Steven (1983-09-01). "Paradoxes of Preferential Voting". Mathematics Magazine. 56 (4): 207–214. doi:10.1080/0025570X.1983.11977044. JSTOR 2689808. Retrieved 2024-05-02.

[:1-8] Volić, Ismar (2024-04-02). "Duverger's law". Making Democracy Count. Princeton University Press. Ch. 2. doi:10.2307/jj.7492228. ISBN 978-0-691-24882-0.

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