Favorite betrayal criterion: Difference between revisions

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== Current Definition of FBC: ==

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An interpretation of this criterion applied to votes as cast is the [[Sincere Favorite criterion]].

=== Favorite Betrayal Criterion video ===

Favorite betrayal in [[plurality]] and [[instant-runoff voting]]:

A video titled "How our voting system (and IRV) betrays your favourite candidate" by Dr. Andy Jennings at Center for Election Science explains favorite betrayal in [[plurality]] and [[instant-runoff voting]]:

<youtube>JtKAScORevQ</youtube>

Jennings refers to the dominant sample parties as the "Good Party" and "Bad Party", where the "Good Party" frequently beats the "Bad Party" candidate 55% to 45%. Then a new third party emerges: the "Ideal Party", a small set of voters who prefer the Good Party to the Bad Party. A voter that prefers the "Ideal Party" to the "Good Party" will naturally want to rank:

#Ideal Party

#Good Party

#Bad Party

This works well, so long as the "Ideal Party" doesn't get very popular, and the Ideal Party voters rank the Good Party as their second choice (thus ensuring that the Good Party candidates

However, if the "Ideal Party" gets popular, then the Ideal Party candidate can cause the Good Party candidate to get eliminated. If the '''all''' of the voters that prefer the Good Party ranked the Ideal Party candidate as their second choice, then the Ideal Party candidate can still win. But it only takes a small portion of Good Party voters to tip the election to the Bad Party candidate by voting these preferences:

#Good Party

#Bad Party

#Ideal Party

== Acknowledgements ==

''Some parts of this article are derived with permission from text at http://electionmethods.org''