[EM] Endorsement for STAR voting

[Closed Limelike Curves]

I think Kris is mostly correct when he says this:
>
> Over time, this incentive to entry could reduce STAR to Range.

but I see this as intentional. Score and approval are great systems on
their own. They elect Condorcet winners in the presence of strategy, but
score does *better* than Condorcet if voters are honest. They satisfy
sincere favorite, IIA, and rarely incentivize order reversal. It's hard to
design something better that won't hurt the average voter's brain.

I expect that as soon as STAR is a thing, parties will start nominating
candidates in pairs. This is good; it gives voters more choices. STAR is a
two-step procedure, where first you hold a score vote to pick the
frontrunners (because the first round is score), and then you hold what's
effectively an approval vote to pick the single best candidate.

It's fun to imagine more complex voting systems, but I've come to recognize
an iron law of voting systems: *every sufficiently well-designed voting
system converges to score*. We have an impossible trilemma:
1. If your voting system doesn't respond to strategic exaggeration, it's
not responsive to voters. (If you rank a candidate 1st, they damn well
*should* do better than if you put them in the middle!)
2. If it responds to exaggeration but penalizes compression (ranking
several candidates first makes them less likely to win, compared to ranking
them all), it's Duvergerian (favorite-betrayal incentive).
3. If it responds to exaggeration but doesn't penalize compression, it's
approval voting (at least if you have strategic voters).

Of these, it seems like voting theorists have converged on #3 being the
least-bad option, although some systems try to compromise.

STAR tries to compromise between 2 and 3, but mostly sticks close to 3. It
has a favorite-betrayal incentive, but it's negligible. (Only possible if
the score-runner-up without your vote would win the runoff, but the
score-runner-up with your vote would lose). It also gives slight
decompression at the top end (sometimes you'll want to rate 4 stars instead
of 5, to make sure your favorite beats your second-favorite).

The only way I can see us moving past this trilemma is if we have some
outside-the-box mechanism. We can't *just* look at vanilla voting systems
that pick the best candidate from a pool. We need to look at mechanisms
that make support costly *across *races or decisions. Voters need to be on
the hook if they try to just top-rate all their favorites, but that
incentive has to come from paying a cost somewhere *other* than inside the
race. If you try to make it costly to support multiple candidates at once
(like cumulative voting does), you just get favorite-betrayal and plurality
again.

Improvements on approval voting will probably come from some direction like
working out how to make the VCG mechanism more resistant to coalitions and
letting voters rate candidates across multiple races. Most decent voting
systems are already up against the brick wall of top-shelf methods labeled
Score/Approval/STAR/RP/Tideman alternative—notice that all of these except
STAR were proposed more than 30 years ago, all give similar results in
practice, and we *still* haven't figured out a way to beat them!

On Tue, Mar 19, 2024 at 5:31 AM Kristofer Munsterhjelm <km_elmet at t-online.de>
wrote:

> On 2024-03-19 02:05, Rob Lanphier wrote:
> > Hi folks
> >
> > I was asked to provide a quote supporting STAR voting by the Equal.Vote
> > Coalition (equal.vote <https://equal.vote>).
>
> [snip]
>
> > I think the Condorcet winner criterion (CWC) matters a lot more than
> > "cardinal" advocates often suggest, but it's almost impossible for me
> > to imagine a credible election scenario where the STAR winner and a
> > strictly CWC-compliant method would differ.   More to the point, with
> that final
> > pairwise comparison, STAR virtually guarantees that a majority of voters
> > prefer the winner to the runner up.  And it's 1000% better than RCV/IRV
> > as promoted by FairVote.
>
> The obvious thing that comes to mind that could make STAR fail Condorcet
> is the clone problem. It doesn't even have to be a deliberate strategy:
> it could just emerge from the incentives. Suppose that there are three
> parties: Left, Center, and Right. Say that Left often is the Range
> winner, but the Left-first voters is a minority so Center comes in
> second and wins the runoff.
>
> Then a second near-Left party has an incentive to grow, because if it
> can get strong enough, it knows that the left voters will also give it a
> high rating, so that the runoff now consists of two left-wing
> candidates, and thus one of them will win. If the rules permit a party
> to field multiple candidates, then it's even easier: the existing Left
> party can just field two.
>
> Over time, this incentive to entry could reduce STAR to Range.
>
> I agree that if we are to take strength of preference seriously (in the
> vNM sense, as I described in my other post), then it should, as you put
> it, take nuance into account, but not too much of it. I have some
> thoughts about how that could be done (I've written posts about it), but
> the methods would be considerably more complex.
>
> Or if you're on the ordinal side of the divide,
> Smith//Range(renormalized) would fix the clone problem for rated clones.
> But it wouldn't be monotone.
>
> The clone problem and entry incentive could be detected by simulation by
> replicating James Green-Armytage's work in the paper where he showed
> that IRV has an exit incentive. To my knowledge, nobody has done so yet,
> which would explain why you haven't seen any simulations of that form.
>
> -km
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>
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