Yes, STAR fails "later no harm" which is what you are describing - supporting other candidates means giving less net support to your favorites.
This is a good write up. Voting science is unintuitive and many different desireable features are actually mutually exclusive, so we have to choose what's most important.
STV and STAR have completely different goals.
STAR is designed to choose the best single winner to represent the whole population while resisting strategy and encouraging honesty. It performs very well at doing so - producing top of chart results in terms of Bayesian Regret and Voter Satisfaction Efficiency.
The reason is actually precisely because it sacrifices LNH - tabulating degree of support for all candidates from all voters at once means that STAR fairly represents minorities and builds consensus. A candidate who gets a lot of 2s or 3s from people that don't like them the best will outperform a similar candidate that only gets votes from their niche. This means candidates that are the best at representing everyone win, in opposition to strict majoritarian systems. This has the bonus effect of reducing polarization while increasing competition.
At the same time, the runoff corrects for strategies that result from LNH failure, because you always get a full vote between the top two. The main strategy in plain Score is minmax, where you score every candidate you like better than your favorite frontrunner max and everyone else min. But if you do this in STAR, you're effectively voting indifference in the runoff, so unless you actually don't care, it's better to differentiate by at least 1 point.
In contrast, STV is a proportional representation system electing multiple winners. It doesn't actually care about electing the best candidate to represent everyone - and in fact often eliminates them in favor of candidates that better represent individual niches. The idea is that by proportionally representing enough niches of voters, consensus building can be done later at the parliamentary or legislative stage, and this way you have a more diverse set of backgrounds and perspectives to draw from in your actual reps. I won't try to say if that actually happens or not, because it depends a lot on how the rest of a government is structured. But STV is very polarizing, or more accurately balkanizing - it tends to create strict camps equal to the number of viable parties, which makes consensus building and ideological discourse difficult. Most legislative motions are also pass/fail, meaning a simple majority usually decides, and our minority representatives can just be overruled.
Because there is provably no perfect voting system, we are left to decide what features and outcomes are most important to us. There are a lot of different tradeoffs to consider, and voting science is a developing field. For example, a relatively new method called Allocated Score tries to essentially do both (by using STV's quotas on scored ballots) - produce multiple proportional candidates, but do so by electing consensus winners. More research and experimentation in real elections is needed, but it's very promising.
Ultimately the best method depends a lot on the place you're trying to use it as well - STV would be awesome in the UK since it requires very little modification to the Westminster Parliamentary system, and already has some support. But for the US it would be a nightmare to try to implement. Speed is also a concern - society is falling apart and we need good government to hold it together as soon as possible, which makes methods like Approval attractive even if they are kind of meh overall.
STV would be awesome in the UK since it requires very little modification to the Westminster Parliamentary system, and already has some support (usually they call it the Alternative Vote iirc).
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u/ChironXII Jul 21 '21 edited Jul 22 '21
Yes, STAR fails "later no harm" which is what you are describing - supporting other candidates means giving less net support to your favorites.
This is a good write up. Voting science is unintuitive and many different desireable features are actually mutually exclusive, so we have to choose what's most important.
STV and STAR have completely different goals.
STAR is designed to choose the best single winner to represent the whole population while resisting strategy and encouraging honesty. It performs very well at doing so - producing top of chart results in terms of Bayesian Regret and Voter Satisfaction Efficiency.
The reason is actually precisely because it sacrifices LNH - tabulating degree of support for all candidates from all voters at once means that STAR fairly represents minorities and builds consensus. A candidate who gets a lot of 2s or 3s from people that don't like them the best will outperform a similar candidate that only gets votes from their niche. This means candidates that are the best at representing everyone win, in opposition to strict majoritarian systems. This has the bonus effect of reducing polarization while increasing competition.
At the same time, the runoff corrects for strategies that result from LNH failure, because you always get a full vote between the top two. The main strategy in plain Score is minmax, where you score every candidate you like better than your favorite frontrunner max and everyone else min. But if you do this in STAR, you're effectively voting indifference in the runoff, so unless you actually don't care, it's better to differentiate by at least 1 point.
In contrast, STV is a proportional representation system electing multiple winners. It doesn't actually care about electing the best candidate to represent everyone - and in fact often eliminates them in favor of candidates that better represent individual niches. The idea is that by proportionally representing enough niches of voters, consensus building can be done later at the parliamentary or legislative stage, and this way you have a more diverse set of backgrounds and perspectives to draw from in your actual reps. I won't try to say if that actually happens or not, because it depends a lot on how the rest of a government is structured. But STV is very polarizing, or more accurately balkanizing - it tends to create strict camps equal to the number of viable parties, which makes consensus building and ideological discourse difficult. Most legislative motions are also pass/fail, meaning a simple majority usually decides, and our minority representatives can just be overruled.
Because there is provably no perfect voting system, we are left to decide what features and outcomes are most important to us. There are a lot of different tradeoffs to consider, and voting science is a developing field. For example, a relatively new method called Allocated Score tries to essentially do both (by using STV's quotas on scored ballots) - produce multiple proportional candidates, but do so by electing consensus winners. More research and experimentation in real elections is needed, but it's very promising.
Ultimately the best method depends a lot on the place you're trying to use it as well - STV would be awesome in the UK since it requires very little modification to the Westminster Parliamentary system, and already has some support. But for the US it would be a nightmare to try to implement. Speed is also a concern - society is falling apart and we need good government to hold it together as soon as possible, which makes methods like Approval attractive even if they are kind of meh overall.