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Yes, I understand how IRV works, and indeed I used to believe it was flawless. >There is no way that placing your preferred candidate first can ever result in
by aninhumer 11y ago
Yes, I understand how IRV works, and indeed I used to believe it was flawless.
>There is no way that placing your preferred candidate first can ever result in your vote not being given in the order you choose.
No, but it can end up harming your second choice, by eliminating them early, so your vote for them doesn't matter. This is called Favourite Betrayal, and it's a serious problem with IRV:
https://www.youtube.com/watch?v=JtKAScORevQ https://www.youtube.com/watch?v=JtKAScORevQ
And as a quick worked example, if you have 4 people voting A>B>C, 4 people voting C>B>A and 3 people voting B>A>C, then A wins. If one person voting C>B>A changes their vote to B>C>A, then B wins. So by putting C first, they were harming their second choice B.
- danieltillett 11y agoThese type of contrived examples appear to occur rarely in practice. I would love to see some bootstrap simulations on real IRV elections results to see how sensitive IRV is to these pathological outcomes. Most of the time you are only interested in which of the major candidates gets your second choice.
- aninhumer 11y agoI don't know if they're that contrived. The scenario is that you have a closely matched two party system (as most FPTP places do) and a third party which is close in popularity to one of the mainstream ones on first votes, but is not universally supported by the remaining mainstream voters over the other mainstream party. That doesn't just sound plausible, it sounds like exactly the pattern of growth for a third party that you'd expect.