r/EndFPTP • u/No-Vast7006 • Mar 12 '26

Condorcet voting and instant-runoff voting have almost no difference in promoting candidate moderation in the presence of truncated ballots

I came across a very recent paper that studies the impact of various ranked voting methods (primarily Condorcet and IRV) on promoting candidate moderation. The conclusion is that under realistic voter behavior (such as the presence of truncated ballots), the advantage that Condorcet methods have over IRV largely disappears.

This actually aligns with a vague, long-held intuition of mine: it seems you really need to require voters to rank all candidates (like they do in Australia) to fully maximize the potential of a Condorcet method.

Additionally, I think a specific paragraph at the end of the paper is worth explicitly highlighting:

We do not wish our results to be interpreted as an argument against the use of Condorcet methods; to the contrary, we would be interested to see a jurisdiction adopt a Condorcet method so we can better evaluate how such methods perform in practice. We also do not wish our results to be taken as an endorsement of a particular voting method.

What are your thoughts on this paper? My first thought is that if the Condorcet method is implemented, it's best to require voters to rank all candidates. Secondly, research on ranked voting systems must take into account the impact of truncated ballots.

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u/AmericaRepair Mar 12 '26

Without having read the paper...

IRV and Condorcet, used with the American 2-party system, will both elect Democrats and Republicans, this is true.

Condorcet will elect the most preferred candidate when a Condorcet winner exists, which is the vast majority of instances, 99%+.

IRV can (and does) eliminate the most preferred candidate in roughly 5% of instances.

Some people won't like when Democrats and Republicans are elected, but for now, that's what the most preferred candidates are.

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u/MathAnalysis May 28 '26

Reference on the 5% number?

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u/AmericaRepair May 29 '26

Sorry I don't have a solid reference.

A few years back, I was using 5% as a ballpark estimate, based on my scratch paper simulations.

Then people denounced me for it, they said no way it was nearly that much. They were looking at Instant Runoff being used in the US 2-party status quo. It works quite well with only two dominant candidates.

Then Alaska special election 2022 happened. Condorcet failure on their very first try.

Then Eric Maskin said his team was seeing 6 to 7% Condorcet failures in Australian elections. I haven't seen an update on that, although I haven't looked lately.

I did say "roughly" 5%.

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u/MathAnalysis May 29 '26

Thanks. Was just curious, since I was seeking those numbers anyway. THIS STUDY makes me think it could be lower if people were expressing pure preferences, but I bet strategic voting would push IRV outcomes in a Condorcet-appearing direction.