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ELI5: why do we care about Condorcet failures? From https://fivethirtyeight.com/features/what-democrats-win-in-alaska-tells-us-about-november/ https://fivethir
by theptip 4y ago
ELI5: why do we care about Condorcet failures?
From https://fivethirtyeight.com/features/what-democrats-win-in-alaska-tells-us-about-november/ https://fivethirtyeight.com/features/what-democrats-win-in-a...
> 40 percent of voters had chosen Peltola as their first choice, 31 percent had chosen Palin and 29 percent had chosen Republican businessman Nick Begich III. Under the rules of ranked choice voting, Begich — as the candidate with the fewest first-choice votes — was then eliminated, and his votes were redistributed to whomever his voters ranked second.
> Unsurprisingly, most of Begich’s votes (50 percent) went to his fellow Republican, Palin. But an impressive 29 percent went to Peltola, and 21 percent were “exhausted,” meaning there was no second-choice pick, and the votes were essentially thrown out. That combination was enough for Peltola to win. While Palin gained more votes from the redistribution than Peltola did, Peltola was starting from a higher total, and receiving 29 percent of Begich’s votes was enough to keep her ahead of Palin. In the end, Peltola received 51 percent of the votes counted in the final round, while Palin received 49 percent.
Sounds fair to me. Some of Begich’s voters expressed a “Begich or nobody” preference. Many Begich voters expressed a “Peltola over Palin” preference. It’s not clear to me why pairwise preferences are meaningful, they don’t encode nuances like the above. Though maybe that’s a feature and not a bug?
I’m aware this gets pretty technical with Arrow’s theorem, maybe there isn’t an ELI5.
- burlesona 4y agoThe problem with IRV is that it asks for a full list of preferences but doesn’t actually respect the voters full preference, and specifically it violates monotonicity. This short video gives an example that’s easy to understand: https://youtu.be/Xekj6gycFpU?list=PLz0n_SjOttTcmP-7y4beuYv49L3qiRtwn https://youtu.be/Xekj6gycFpU?list=PLz0n_SjOttTcmP-7y4beuYv49...
- theptip 4y agoMonotonicity intuitively seems like it would be desirable, but I'm struggling to see how the effect described in the video actually matters in practice. It seems vanishingly unlikely that candidates 2&3 would be eliminated in a tie (and you can just change the rules to force a re-vote/runoff in that case if you really think it's a bad outcome, similar to how you'd handle a tie in FPTP). And even then, the outcome of picking the first candidate when 2&3 are tied doesn't seem explicitly unfair. I'm sure there are other cases where this can show up too though, and maybe some of those do seem unfair. I can see how ex post, one could say "if I had ranked my choice lower, they would have done better", but it's not clear to me that this property actually informs any real-world voting strategy ex ante. Basically, this seems like a somewhat academic property that most voters probably wouldn't care about, so it's not clear that a lack of monotonicity would actually impede IRV from popular acceptance.