[EM] Re: equal rankings IRV

[Kevin Venzke]

Bart,

--- Bart Ingles <bartman at netgate.net> a écrit : > 
> > The simplest FBC failure scenario I can think of looks like this:
> > 
> > 6 A
> > 2 B
> > 2 C=B  <<< (sincere is C>B)
> > 3 C>B
> 
> I don't think this is a particularly obscure example.  Suppose A is the
> incumbent, with B and C members of a split challenging party.  This
> scenario seems all too common.  The only thing missing are the A-leaning
> swing voters, who lean B>>A>C.

I think it would be rare if the voters understood the method.  If the method
were Approval, and the C>B voters just approved C, we wouldn't hesitate to
say that those voters aren't voting optimally.

> > Reasoning: If lesser evils never have lower preferences, only first preferences,
> > then A is either going to have more votes than B or he isn't.  Eliminating
> > other candidates isn't going to change that.
> 
> Right-- if they vote as though it were straight approval voting.  I
> agree.  This is why consider approval voting a better system than
> ER-IRV(whole).

I don't disagree with that.  I'm only arguing that ER-IRV(whole) is much better
than FPP, IRV, ER-IRV(fractional), runoffs, etc., in avoiding the Duverger scenario.

> > I think for the C=B voters to vote B>C, they would have to believe that C
> > can't beat A, and that despite this, more voters will vote C>B than B.
> 
> Well, it's true, isn't it?  So all they need is an accurate poll.

By "despite this" I mean to imply that the C>B voters are clearly voting in
an unwise way.

> It might be reasonable to assume that if the B=C voters didn't have the
> ER option, some would strategically rank B first and some would
> sincerely rank C first.  If half-and-half, ER-IRV is neither better nor
> worse than plain IRV.

I don't understand what you're saying here; if they don't have the ER option
then the method is equivalent to plain IRV.

I definitely don't agree that voters would *typically* have good reason to
place their compromise in sole first place.  If your favorite is capable
of getting more first-place votes than your compromise, I doubt it could be
so clear that your favorite isn't a front-runner after all.  It could be
that the strategic order reversal is what spoils the election, and this wouldn't
even require other voters' help.

> On the other hand, the fact that they voted B=C might indicate that they
> were inclined to vote strategically anyway.  It's clear that these two
> voters would have been better off voting B>C, so maybe they would have
> voted that way.

Maybe, but in my view that would involve insincerity whereas compression
wouldn't.

> With approval voting, it might be reasonable to assume that some of the
> C>B>A voters would have voted C=B (with the remainder bullet voting for
> C).  If two of these voted C=B in the example above, the outcome would
> have changed.

In my view, with ER-IRV(whole), it might be reasonable to assume that a
C>B>A voter would vote C=B.  That they didn't, makes as much sense to me
as bullet voting for a dark horse in Approval.

> > I think the voters risking the election are those who DON'T use approval
> > strategy.
> 
> I don't think that's a valid generalization.  The statement is true
> enough for the more extreme voters, who voted C>B, but in this case the
> voters who DID use approval strategy were the ones who blew the
> election.

I don't see how one can say that it was the C=B voters and not the C>B
voters who blew the election.  The C>B vote, on its face, is worse strategy
than the C=B vote.  The Favorite=LesserEvil vote is not capable of blowing the 
election unless some voters hide their support for the LesserEvil.

>    Note that the C>B voters were ranking sincerely, while the
> B=C voters were apparently attempting to use strategy (they just didn't
> use a strong enough strategy).

So if you voted sincerely, you're not responsible for blowing the election??

> > --- Bart Ingles <bartman at netgate.net> a écrit : >
> > > What would convince me otherwise would be a set of strategy equations
> > > comparable to those used for calculating optimal strategy in approval
> > > voting, or possibly simulations with ER-IRV(whole) showing that
> > > "lesser-evil or better" strategy is as good or better than
> > > "lesser-evil-only" in terms of social utility efficiency.
> 
> Another thought-- has anyone calculated the best zero-info strategy
> under ER-IRV(whole)?  Is it to rank sincerely, use approval strategy, or
> something in-between?

I imagine it is mostly approval strategy, but perhaps some very low utility
compromises could go in second place.

I'm fairly sure it could be shown that if you strictly rank, the risk of causing
your compromises to be eliminated would be much more expensive than whatever utility
cost you pay by not differentiating among your "approved" candidates.

> > Well, I can't produce these, at least not at the moment...  But my thoughts
> > would be:
> > 
> > "Lesser-evil-only" will only elect lesser evils.
> > "Lesser-evil or better" could elect a more broadly appealing candidate, just
> > as in Approval.
> 
> The problem is that the C>B>A voters mistakenly believed that ranking B
> second was enough.  This was a kind of a "sucker bet", much like giving
> a partial rating under Cardinal Ratings.  Then again, the C=B>A voters
> were also commiting a "sucker bet".  It's not that they were wrong-- you
> can be wrong in approval voting too-- it's that they were'nt maximizing
> their chances.

This "sucker bet" idea is why I think you should not strictly rank in zero-info.
Although I don't see how C=B is also a sucker bet.  Is it always a sucker
bet to use compression strategy?

> > Again, if people are using "lesser-evil or better" strategy, I don't know
> > where the FBC failures come in.
> 
> You did a good job of illustrating one above; I think where we differ is
> the likelihood of it happening.

Well, I thought the simulations would assume that everyone used a certain strategy.
When everyone puts a lesser evil in first (even if tied), there is no FBC problem
as far as I can see.

> We haven't touched on nomination strategy, but if the B and C were
> members of the same party, it would be in the interest of the party to
> make sure that C was kept off the ballot.  Hence the Duverger effect.

That's true in Approval, too.  In ER-IRV(whole), the party has to ask for less than
it would in Approval: It needs all its supporters to either equal-rank B=C or to
rank B>C or C>B.  From this perspective, it's the 2 B voters who have wrecked the
result.

In Approval, the party needs everyone to vote B=C.  Probably easier to ask C
to bow out, don't you think?

I don't think this is a big deal, though, since if B and C belong to the same
coordinated party, I don't think that their being able to simultaneously stand
for election (without spoiling the result) would be evidence of there not being
a Duverger effect.

Kevin Venzke
stepjak at yahoo.fr


	

	
		
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