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Instant-runoff voting: Difference between revisions

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Instant-runoff voting (view source)

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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': 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 histheir 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 histheir actual first choice.
 
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:
The following example is given on [[http://electionmethods.org/ ElectionMethods.org]]:
:Suppose my true preference is for the Libertarian first and the Republican second. Suppose further that the Libertarians are the strongest "minor" party. At some round of the IRV counting process, all the candidates will be eliminated except the Republican, the Democrat, and the Libertarian. If the Libertarian then has the fewest first-choice votes, he or she will be eliminated and my vote will transfer to the Republican, just as I wanted. But what if the Republican is eliminated before the Libertarian? Unless all the Republican votes transfer to the Libertarian, which is extremely unlikely, the Democrat might then beat the Libertarian. If so, I will have helped the Democrat win by not strategically ranking the Republican first.
 
# Ideal Party
However, this thinking is flawed. The problem in this case is that the Republicans are not the major party, but the third party. They come in third, that makes them a third party. And they fail to vote second for their Libertarian second choice, so their second choice does not win. This is how it is supposed to work. When third-party voters don't vote for their second choice, the second choice might not win. The proposed solution is that the major-party voters should vote third-party first.
# 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
Try this reasoning when Republicans are the major party. They think that Libertarians will not vote Republican second, and there are enough Libertarians to keep the Republicans from winning. So -- even when they have 45% of the vote and Libertarians have 6%, Republicans might agree to vote Libertarian because they would prefer Libertarians to Democrats. Does that sound in any way plausible? So why would major-party Libertarians vote third-party on the assumption that the third-party voters won't vote second for their candidate? Because they have no self-respect.
 
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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