Instant-runoff voting: Difference between revisions
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(→Return of the '3rd-party spoiler effect': replacing the Republican/Libertarian example with "Good/Bad/Ideal" example from CES video. See talk) |
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==== Return of the '3rd-party spoiler effect' ==== |
==== Return of the '3rd-party spoiler effect' ==== |
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IRV only stops the '3rd-party spoiler effect' as long as the 3rd party clearly does not have a chance to win. Just when the 3rd party grows to a competitive size, voters may start to find again that they benefit from tactically ranking a major party candidate over their favorite candidate. |
<blockquote>''main article: [[Favorite betrayal criterion]]''</blockquote>IRV only stops the '3rd-party spoiler effect' as long as the 3rd party clearly does not have a chance to win. Just when the 3rd party grows to a competitive size, voters may start to find again that they benefit from tactically ranking a major party candidate over their favorite candidate. |
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This failure mode occurs if the voter fears that their 1st-choice candidate (the 3rd party) might first win from his best-liked major party, then not get enough of the redistributed votes, and finally almost certainly lose to the other major party. The voter would wind up with his least-favored outcome. The voter may seek to prevent this by ranking the best-liked major party over their actual first choice. |
This failure mode occurs if the voter fears that their 1st-choice candidate (the 3rd party) might first win from his best-liked major party, then not get enough of the redistributed votes, and finally almost certainly lose to the other major party. The voter would wind up with his least-favored outcome. The voter may seek to prevent this by ranking the best-liked major party over their actual first choice. |
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This problem is known as "[[Favorite betrayal|favorite betrayal]]". A video which explains this problem more is [https://www.youtube.com/watch?v=JtKAScORevQ "How our voting system (and IRV) betrays your favourite candidate" by Dr. Andy Jennings at Center for Election Science], and an overall summary of [[Favorite betrayal criterion]] can be found on this wiki. |
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# Ideal Party |
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# Good Party |
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# Bad Party |
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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 |
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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: |
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# Good Party |
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# Bad Party |
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# Ideal Party |
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==== Failure to pick a good compromise ==== |
==== Failure to pick a good compromise ==== |
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