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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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.
This failure mode occurs if the voter fears that
There's a video that explains this well: [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]. 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
==== Failure to pick a good compromise ====
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