[EM] Why I think IRV isn't a serious alternative 2

[Kevin Venzke]

Hello,

--- En date de : Mar 16.12.08, Abd ul-Rahman Lomax <abd at lomaxdesign.com> a écrit :
>However, in defense of Venzke, he thinks that the situations where IRV 
>is non-monotonic are rare enough that it's not worth worrying about.

What I think would be rare is that such situations (or the risk of such
situations) would have any effect on voter behavior.

>The real bite is with Center Squeeze.

I agree with this.

--- En date de : Mar 16.12.08, Abd ul-Rahman Lomax <abd at lomaxdesign.com> a écrit :
> > Thus, *all things being equal* (which must
> > be kept in mind if it's IRV that is on your mind),
> I would expect that
> > failing LNHarm will provoke more insincerity (and thus
> destroy more
> > information) than failing monotonicity.
> 
> Highly speculative. Bucklin probably experiences about the
> same level of bullet voting due to LNH fears as IRV, not
> much more, because the "harm" only happens when a
> majority isn't found in the first round.

If methods typically won't require more than the top rank, then I guess
neither LNHarm nor monotonicity failures will be much of a problem.

>In other words, Center Squeeze is a direct consequence of LNH compliance
>by IRV.

Well, MMPO satisfies LNHarm, and is nearly a Condorcet method.

>Interesting, eh? Top three. A Condorcet winner is almost certainly in 
>there!

I think this is doubly likely if you arrange the incentives so that it's
likely that third place achieved that position better than randomly.

In other words: I want to have a TTR election where candidates risk being
spoilers if they place worse than third.

This places part of the election process outside of the election itself,
but we already do this with Plurality.

>From the first message:

> "Frontrunner strategy" is a common one that seems
> to help with ranked methods as well as Range ones. Make sure
> you cast a maximally effective vote for a frontrunner, and,
> where "against" matters, against the worst one.
> Usually there are only two frontrunners, so it's easy.
> "Expectation" is actually tricky if one
> doesn't have knowledge of the electorate's general
> response to the present election situation. How do you
> determine "expectation." Mean utility of the
> candidates is totally naive and non-optimal.

Mean utility is supposed to be naive, and it is optimal, if you are
"naive" about win odds.

"Better than expectation" is mean *weighted* utility. You weight the 
utilities by the expected odds that each candidate will win. (There is 
an assumption in there about these odds being proportional to the odds 
that your vote can break a tie.)

"Frontrunner strategy" is just a special case of "better than 
expectation," where only two candidates are expected to have any chance
of winning.

> But it's a complex issue. My point is that "better
> than expectation" has been taken to mean "average
> of the candidates," which is poor strategy, any wonder
> that it comes up with mediocre results?

"Average of the candidates" is the special case of "better than
expectation," where there is no information on candidates' win odds.

> > The big concern is what happens when poll stability
> can't be achieved.
> 
> Nah! Most voters won't pay that much attention to
> polls, they will just vote their gut. Polls will be used by
> those who are very seriously involved, who want to maximize
> the power of their vote. I think most of the "big
> concern" is simply imagination. There won't be big
> surprises with Approval. Little ones, sure.

I use the term "polls" loosely. It is hard to imagine that under any
election method, voters in this recent election might not have realized
that the important contest was McCain vs. Obama.

If voters "vote their gut" and don't consciously use any strategy, I'd
say this will be well beyond the point where polls have already taken 
their toll and removed unviable candidates from the voters' 
consciousness.

I absolutely want voters to pay attention to polls, because if they don't,
this is probably the same as the polls being unable to stabilize around 
two frontrunners. And the results of such elections would be rather 
arbitrary, I would guess.

> In plurality
> Approval, strategy based on polls would loom larger. Sure,
> it could oscillate. But how large would the osciallations
> be? 

The only situation I'm concerned about is where, when the polls report
that A and B are the frontrunners, this causes voters to shift their
approvals so that the frontrunners change, and when the polls report
this, the voters react again, etc., etc. Obviously it wouldn't be as
neat as that (in my simulation, not everyone is allowed to change their
vote at the same time; they receive random opportunities). But I guess
the result is that there would ultimately be more than two frontrunners 
in the voters' consciousness.

> And, in the end, the winner is the candidate accepted by
> the most voters. 

But when one (such as myself, and I think also you) portrays Approval as
a strategy game, under which "sincerity" is a red herring, a statement
like the above falls very flat. What does it mean to be "accepted" by the
most voters?

If candidates were at least obtaining majority approval, I could be
content with the statement. But if no one obtains a majority, offering as
consolation that the most "accepted" candidate won is not much more
comforting under Approval than under Plurality.

> It's not going to be a terrible result,
> if Approval falls flat on its face, it elects a mediocre
> candidate because the voters didn't get the strategy
> right.

Well, what is a "terrible result" after all? It seems to me you don't 
have to be too picky to find methods that only fail by electing mediocre 
candidates.

> > I did simulate MCA, and yes, the D voters continued to
>> vote for D as their favorite (they were not allowed to list
>> multiple favorites, but this was simply to make the coding
>> more manageable). I don't know what you mean by voters
>> not giving up so easily as my simulated ones. How easy is
>> easy? I could conceivably program some voters to insist on
>> being sincere. (In whatever sense that it is not sincere to
>> vote also for C.) But it seems to me that this type of voter
>> is a bad thing for Approval, just as it is under Plurality.
> 
> What type of voter is bad for Approval? Easy compromiser or
> tough bullet voter?

The type of voter who is willing to cast a suboptimal vote due to 
principle. It is harmful under Plurality and here is a situation where
it would be harmful under Approval.

Kevin Venzke