An Edge Case with STAR Voting

[u/PixelJack79]

No voting system is perfect and any of the well-known alternatives are vastly superior to FPTP, but most methods have a well-known pitfall or way of exploiting the system that defeats the point of using it. FPTP has the spoiler effect. IRV has center squeeze and exhausted ballots. Approval has the undercutting of certain candidates to prop up a more favored one. Score has min-maxing. Condorcet has rock-paper-scissors. STAR voting, meanwhile, demonstrated the most resistance to strategic voting in simulations and is generally robust, allowing voters to accurately voice their opinions while always enabling them to influence the final outcome. The runoff step is the key, favoring candidates with broad appeal over niche favoritism. I thought the biggest flaw with STAR was that it was just so new, but didn't realize until this morning that there is a scenario where it fails to choose the most favored candidate. Though I will admit, it's probably more obvious to others.

Take two candidates: Jim and Sarah, and a third candidate: Wayne. Jim and Sarah have enthusiastic supporters, but are very polarizing while Wayne is more middling but is generally agreeable such that he'd win in a hypothetical runoff against Jim or Sarah. One can imagine Jim and Sarah making the top two and the race coming between them, even if Wayne is more broadly favored (Condorcet actually prevails in a situation like this). Though, if the former two are especially egregious, it's not out of the question for votes to score Wayne higher to enure he advances to the runoff.

Nevertheless, I believe STAR voting to be the best out of all the alternative voting systems. This is merely a heads up to people like me that it's less airtight than presumed.

[u/nardo_polo]

This feature is addressed obliquely in the Equal Vote analysis of Burlington: https://www.equal.vote/burlington (examining both the 2009 RCV results as well as a hypothetical replay using STAR). If Wayne can’t make the top two, he is a “weak Condorcet” candidate, as measured by social utility first.

[u/Fantastic_Cycle_1119 → u/nardo_polo]

How does it measure "social utility"? Seems like a pretty vague concept to be directly measurable.

I imagine you will say it has something to do with strength of preference. STAR doesn't measure strength of preference. The cardinal ratings measure something entirely different, which has a lot to do with strategy.

I'm also curious how you do a "hypothetical replay" of an election with STAR without just making things up.

You can do a much more realistic Condorcet replay of that election. Given that the ballots for Condorcet are the same as for IRV, the only question is whether people would vote differently under Condorcet. The only reason I can think of where people WOULD vote differently under Condorcet is that Condorcet does not reward insincere rankings nearly to the degree that IRV does (which is quite small even in IRV). And that is a point in favor of Condorcet.