[EM] STAR

[C.Benham]

Toby,

> Also a run-off between the most two approved candidates still has 
> STAR's clone problem.

Some years ago I suggested that 2-round Top-Two Runoff  could be 
improved by using approval ballots in the first round
and then having a runoff between the most approved candidate (the AW) 
and the candidate with the most approval opposition
to the AW (i.e. is most approved on ballots that don't approve the AW).

> If the most approved candidate is cloned, the run-off becomes irrelevant.
>
Spoken like someone who lives in parliamentist country. "Clones" aren't 
necessarily identical.  There could be slight political differences
or one may be less corrupt, or one could just have a much better haircut.

Parties being having incentive to each field two candidates (even if 
they are "clones") is maybe not too bad.  But STAR uses score ballots
so there is a danger that there being two candidates from the same party 
might cause voters to not give both of them max score enough
to stop both of them from making the final.

> However, I just don't think that STAR's failure here can reasonably be 
> called a monotonicity failure.

I think it is very much like one and it's claiming of bragging rights on 
that point over IRV is unfair and misleading.

Chris




On 20/08/2023 5:55 am, Toby Pereira wrote:
> Also a run-off between the most two approved candidates still has 
> STAR's clone problem. If the most approved candidate is cloned, the 
> run-off becomes irrelevant.
>
> Toby
>
> On Saturday, 19 August 2023 at 17:43:12 BST, Toby Pereira 
> <tdp201b at yahoo.co.uk> wrote:
>
>
> Chris
>
> It's not that I disagree with your views of STAR's behaviour as a 
> method. And there are changes that could be made that would improve 
> STAR, as you say. However, I just don't think that STAR's failure here 
> can reasonably be called a monotonicity failure.
>
> Toby
>
> On Saturday, 19 August 2023 at 04:10:32 BST, C.Benham 
> <cbenham at adam.com.au> wrote:
>
>
> Toby,
>
>> I wouldn't count this as a monotonicity failure because it involves 
>> decreasing Y's score as well as increasing X's.
>
>
> This is like a sophist's technical loophole.  Why do we particularly 
> care about "monotonicity failure"? To avoid some hypothetical mild 
> embarrassment?
> For the sake of marketing bragging rights?
>
> Or because it is related to Push-over strategy 
> incentive/vulnerability?  STAR is much worse in that respect than IRV 
> because there the strategists are entirely
> relying on other voters to both get their favourite into the final two 
> and to there win the pairwise contest, so if too many of X's 
> supporters try the strategy it
> could backfire.
>
> Whereas with STAR the strategists could be a bit cautious and give the 
> weak candidate they are trying to promote into the final a score of 
> max. minus one
> while also giving their favourite X max. points.
>
> That way all of X's supporters could use the strategy and it could 
> still succeed.
>
> The 0-5 score ballot is too restrictive (certainly for STAR)  Say, as 
> I earlier advocated, the voters rank however many candidates they want 
> to and give an approval cutoff wherever
> they want, and we elect the pairwise winner between the two most 
> approved candidates.
>
> That would be very similar to STAR (0-5 score ballots) but wouldn't it 
> be better? And also a method that fails mono-raise and Condorcet and 
> many other criteria
> and is obviously terrible?
>
> Chris
> On 17/08/2023 9:47 pm, Toby Pereira wrote:
> I wouldn't count this as a monotonicity failure because it involves 
> decreasing Y's score as well as increasing X's. Mono-raise may have 
> been defined specifically for ordinal ballots where raising a 
> candidate inevitably pushes others down. Whereas with a rated ballot, 
> I think one would be more likely to define monotonicity criteria in 
> terms of increasing a candidate's score while leaving all others the same.
>
> Toby
>
>
> On Thursday, 17 August 2023 at 05:43:00 BST, C.Benham 
> <cbenham at adam.com.au> <mailto:cbenham at adam.com.au> wrote:
>
>
> Toby Pereira wrote:
>
>> I'm not a fan of STAR, but I am still interested in seeing how it 
>> stands up to scrutiny given that it has a following. (Actually I'm 
>> not aware of how STAR fails monotonicity. I was under the impression 
>> that it passed.)
>>
> Toby,
>
> To give you a bit of a preview before I get around to cooking up all 
> the examples, nothing with such obvious Push-over incentive can meet 
> mono-raise (aka "monotonicty")
>
> Suppose  X beats Y in the final.   Now suppose on some ballots with Y 
> above X, we raise X so it is now above Y. That could reduce Y's score 
> enough for it to be replaced in the final
> by Z, a candidate that pairwise beats X.
>
> Voters who are mainly concerned to have their favourite X win and are 
> fairly certain that X will reach the final will have a strong 
> incentive to give X max points (5) and then also
> give a 4 (or even a 5) to all those candidates that they think X can 
> beat pairwise.
>
> If enough voters use that strategy and it fails, both the finalists 
> could be candidates with little sincere support.
>
> Chris Benham
>
> O
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