Favorite betrayal criterion: Difference between revisions
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The '''favorite betrayal criterion''' or '''sincere favorite criterion''' is a [[voting system criterion]] which requires that "voters should have no incentive to vote someone else over their favorite".<ref>{{Cite web|url=https://rangevoting.org/FBCsurvey.html|title=Survey of FBC (Favorite-Betrayal Criterion)|last=Ossipoff|first=Mike|last2=Smith|first2=Warren D.|date=Jan 2007|website=Center for Range Voting|url-status=live|archive-url=|archive-date=|access-date=2020-04-08}}</ref>
It is passed by [[Approval voting]], [[Range voting]], and [[Majority Judgment]]. All these are examples of [[cardinal voting systems]].
It is also failed by [[Plurality voting]] and two-round [[runoff voting]].
It is defined as follows:
:A [[voting system]] satisfies the Favorite Betrayal Criterion (FBC) if there do not exist situations where a voter is only able to obtain a more preferred outcome (i.e. the election of a candidate that he or she prefers to the current winner) by insincerely listing another candidate ahead of his or her sincere favorite.<ref>Alex Small, “Geometric construction of voting methods that protect voters’ first choices,” arXiv:1008.4331 (August 22, 2010), http://arxiv.org/abs/1008.4331.</ref>
=== Current Definition of FBC: ===▼
▲It is passed by [[Approval voting]], [[Range voting]], and [[Majority Judgment]]. All these are examples of [[cardinal voting systems]]; on the other hand, most [[Ranked voting systems|ordinal voting systems]] do not pass this criterion. For instance, [[Borda Count]], [[Copeland's method]], [[Instant runoff voting]] (IRV, known in the UK as the Alternative Vote), [[Kemeny-Young method|Kemeny-Young]], [[Minimax Condorcet]], [[Ranked Pairs]], and [[Schulze method|Schulze]] all fail this criterion. It is also failed by [[Plurality voting]] and two-round [[runoff voting]].
Michael Ossipoff definition:
▲== Current Definition of FBC: ==
'''Requirements:'''
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A candidate is "top-voted" by you, and is "at top" on your ballot, if you don't vote anyone over him/her.
===Earlier Definition===
The
▲The definiton written below is the one that FBC's initial propponent had originally written and used. Its problem was that it led to the question of "What if the way of voting that optimizes your outcome without favorite-burial is some complicated, difficult-to-find strategy?". That question led to a better definition, written above on this page. Some time ago, someone else, too, had written that definition, and a link to it is given at the bottom of this page, under a different name (Sincere Favorite Criterion).
▲==Earlier Definition==
'''Supplementary Definition:'''
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[[Approval voting]], [[range voting]], [[Majority Judgment]], [[MMPO|MinMax(pairwise opposition)]], [[MCA]] (except MCA-A and some versions of MCA-R), [[MAMPO]], and [[Improved Condorcet Approval]] comply with the favorite betrayal criterion, as do ICT and [[Symmetrical ICT]].
[[Borda count]], [[plurality voting]], [[Condorcet criterion|Condorcet methods]] (except for Improved Condorcet
== Examples ==
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==== Conclusion ====
By voting for their least preferred candidate L instead of their favorite H, the voters changed their favorite from loser to winner and changed the outcome from a least preferred alternative to a more (in this case even the most) preferred alternative. There was no other way for them to accomplish this and still vote for their favorite in the first round. Thus, the two-round system fails the favorite betrayal criterion.
==Commentary==
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=== Favorite Betrayal Criterion video ===
A video titled "How our voting system (and IRV) betrays your favourite candidate" by Dr. Andy Jennings at [[The Center for Election Science|Center for Election Science]] explains favorite betrayal in [[plurality]] and [[instant-runoff voting]]:
<youtube>JtKAScORevQ</youtube>
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#Ideal Party
==
''Some parts of this article are derived with permission from text at http://electionmethods.org''▼
{{fromwikipedia}}▼
* [http://books.google.com/books?id=RN5q_LuByUoC ''Collective Decisions and Voting: The Potential for Public Choice'']
* [http://books.google.com/books?id=i5IPnH1C0hoC ''Chaotic Elections!: A Mathematician Looks at Voting'']
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== References ==
{{reflist}}
▲''Some parts of this article are derived with permission from text at http://electionmethods.org''
▲{{fromwikipedia}}
[[Category:Voting system criteria]]
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