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>they are particularly prone to strategic voting and manipulation? IRV and AV are particularly prone to strategic voting. Amusingly, the best catalog of IRV's
by scythe 6y ago
>they are particularly prone to strategic voting and manipulation?
IRV and AV are particularly prone to strategic voting. Amusingly, the best catalog of IRV's failures is generally provided by AV proponents, and the best catalog of AV problems can be found on FairVote.org.
The ranked-choice systems which satisfy a criterion called ISDA -- independence of Smith-dominated alternatives, or more poignantly, independence of losers -- are harder to manipulate. These are all "Condorcet" methods, because ISDA is a generalization of Condorcet.
ISDA means roughly that if a candidate is not in contention to win (the "Smith set"), it doesn't matter where they appear on your ballot. I could rank Vermin Supreme and Ron Paul #1 and #2 and the algorithm basically cancels it out and starts me at #3. The reason that ISDA is so effective at preventing strategic voting is that in order to vote strategically, I have to misrank a candidate who might actually win; in other words, I must accept a realistic risk of encouraging an outcome I don't really want. That's a pretty good disincentive, in my opinion.
However, the worry about strategic voting seems to be at least a little overblown. Australia does deal with "how-to-vote" cards[1], but this is a way to prevent "allied" parties from accidentally competing with each other. In 2009, there was concern over a monotonicity violation in Australian elections where supporters of one of the parties were encouraged to misrank another party. However, the voters didn't go along with the plan, and instead voted honestly:
https://www.theage.com.au/national/victoria/howtovote-cards-awaken-the-rebel-in-innercity-voter-20101115-17uga.html https://www.theage.com.au/national/victoria/howtovote-cards-...
https://www.abc.net.au/news/2011-05-04/an-example-of-non-monotonicity-and-opportunites-for-tactical-vot/9389768 https://www.abc.net.au/news/2011-05-04/an-example-of-non-mon...