[EM] Meta-criteria 6 of 9: Heuristics. #1, simplicity

[Kevin Venzke]

Hi Juho,

--- En date de : Dim 9.5.10, Juho <juho4880 at yahoo.co.uk> a écrit :
> > You have to give me a reason why I should start with
> > margins or else it won't occur to me.
> 
> See (***) below. That's my best guess on why someone might
> like margins.

I didn't really understand your point below. My question isn't so much
why someone would like margins, but why it would be my starting point.

> > There is no reason to vote "absolutely
> > equal" unless that's just how you sincerely feel.
> Strategically it's
> > like voting 5/10 in Range.
> 
> I agree that mandatory full rankings would collect more
> information and in principle voters that have hard time
> deciding whether A is better than B or not could just flip a
> coin and statistics would balance the situation even if they
> make the wrong decision or are convinced that the candidates
> are equal. Equal rankings are mostly used for convenience.
> On the other hand there is no big reason to ban equal
> ranking either. And especially if there are numerous
> candidates truncation (equal ranking of remaining
> candidates) is a quite natural way to handle the unknown and
> probably irrelevant candidates.

There is no reason to ban equal ranking (in the same way that there is
no reason to ban intermediate ratings in Range) but there is reason to
ban truncation, if it misleads the voters.

If truncation is being used to handle unknown and irrelevant candidates
then the margins interpretation is inappropriate in my opinion. You
don't know who is voting on these candidates and you only partly care
about how many voters are actually involved.

> >> To me the description of minmax(margins) (that
> uses
> >> directly the concept of margins) as "elect the
> candidate
> >> that needs least additional votes to win all
> others" is at
> >> the same time both an exact definition of the
> method and a
> >> description of who would be the ideal winner.
> According to
> >> this philosophy one should elect the candidate
> that would
> >> face least opposition after being elected (by
> people that
> >> would have preferred some candidate X to the
> winner and
> >> could join forces to oppose try to harm the
> elected winner).
> >> I think there are many kind of elections where the
> used
> >> criteria to determine the optimal winner may be
> different.
> >> This philosophy is thus not the only possible
> philosophy but
> >> it is certainly one that could be considered even
> ideal in
> >> some/many single-winner elections.
> > 
> > That's fine. Feel free to use margins where it makes
> sense.
> 
> (***) This was the viewpoint of sincere interest to use
> minmax(margins) because it offers a good utility function
> for certain kind of elections. This utility function can
> also be seen to be a good general purpose single-winner
> election method target (i.e. not just a special solution for
> a special case).

In particular I don't understand why you use the term "utility function."
Does this just mean "method"?

> > For example WV has much better FBC-efficiency than
> margins. I tested this
> > some time ago and would have to find it, but it's easy
> to see why: In
> > margins if you need to weaken a defeat against your
> compromise, you can
> > do it *faster* by just ranking him ahead of your real
> favorite.
> 
> Ok, now we are entering the world of strategy related
> criteria. So far I only tried to justify why margins is good
> with sincere votes. In the area of strategies there are
> vulnerabilities in both directions. Maybe another discussion
> for another day.

We don't have to talk about FBC. My point is that the concerns that
apply to "abstaining" from contests involving truncated candidates are
also relevant to candidates ranked equal.

> > The point is not that WV uses approval, it's that it
> works well with
> > a voter expectation that truncation has a certain
> significance. Maybe
> > the Plurality criterion explains this well enough.
> Maybe the principle
> > that voters would understand actually is approval.
> 
> Plurality criterion is a special criterion since it assumes
> that ranked candidates are somehow approved. I think it
> should not be used on methods that do not make such
> assumptions. In margins pure rankings based approach seems
> to be the normal way to read the ballots.

The difficulty is that I think voters make assumptions more so than
methods.

Anyway, wasn't what I was trying to do, is explain the principle behind
WV? Are you going to reject anything I come up with because it doesn't
work with margins?

> In general I don't like the idea of hidden approval cutoff
> after the ranked candidates very much (or any other positive
> vs. negative borderline after the ranked candidates). That
> is because in general I think that voters should be
> encouraged to give as full rankings as possible in the
> Condorcet methods. 

I know you think that, but I don't think you can do that. You take away
truncation as a sensible option but you don't make it safe to use the
other option. And you are so afraid that people will truncate excessively
but for some reason not afraid about them making a mess of things when
you force them to write down actual preferences about candidates they
are trying to defeat, don't like, or don't know.

> Only the truly irrelevant candidates are
> ones that most voters could just ignore. If voters start
> truncating any potential winners of the competing sections
> then the good properties of Condorcet methods get easily
> lost. The best compromise candidates are no longer
> identified.

It's quite possible that that is dependent on utility, just as with
Approval strategy.

> >>>> P.S. My biggest fears with winning votes
> is that
> >> it might
> >>>> in some real elections (with sincere
> votes)
> >> produce a result
> >>>> that people do not find natural.
> >>>> 
> >>>> 10: A>B=C
> >>>> 20: A>B>C
> >>>> 16: A>C>B
> >>>> 01: B>A=C
> >>>> 01: B>A>C
> >>>> 26: B>C>A
> >>>> 03: C>A=B
> >>>> 03: C>A>B
> >>>> 20: C>B>A
> >>>> 
> >>>> This set of votes is cyclic. B and C are
> from the
> >> same wing
> >>>> (they support each others). But should C
> win (as
> >> in most
> >>>> methods with winning votes) although B has
> more
> >> first
> >>>> preferences than C and also A supporters
> like B
> >> more than
> >>>> C?
> >>> 
> >>> As long as A loses I don't care that much. If
> voters
> >> care so much about
> >>> a 2% difference in FPs then we are generally
> in
> >> trouble. (What principle
> >>> does margins adhere to that prevents this from
> being a
> >> problem in
> >>> general?) And not even half of the A voters
> supported
> >> B.
> >> 
> >> If A represents the left wing then the left wing
> voters
> >> said "we prefer B to C if right wing gets majority
> and one
> >> of their candidates wins". In the left wing there
> were more
> >> voters that didn't maybe care or found all the
> right wing
> >> candidates to be equally bad than in the right
> wing. That is
> >> natural. Within the right wing B seems to be
> clearly more
> >> popular than C, so the right wing agrees with the
> left wing
> >> that B is better than C. The only remaining tricky
> part is
> >> that the votes are cyclic. Can we derive some such
> logic
> >> from that cycle that C should win instead of B?
> > 
> > Why all this talk about B:C, why don't you talk about
> A:B?
> 
> Most methods and we two seem to agree that A should not
> win. (There is the cycle still and that could maybe be used
> to argue something else.)

Yes, I'm talking about the A:B contest, not the idea that A should win.
If the public has such one-sided complaints (and I'm sure they will) we
are in trouble no matter what we put out there.

> > If this scenario is important I can't imagine what
> else is too.
> 
> This scenario is important to me since these votes could
> well materialize in a real life election. Many other example
> threat scenarios on the EM list are ones that are likely to
> occur only in the minds of the election method experts but
> this one could really happen in real life, and regular
> voters and media could start wondering why the method failed
> to see the obvious looking widely spread opinion that B is
> better than C. (This could be a bit like IRV failing to
> elect the Condorcet winner, although maybe not as obvious
> case to argue about because of the involved cycle.)

And A is preferred to B. Yes, the margin is different, but it doesn't
sound like the critics you're talking about are clever enough to even 
see that. If we can't take criticism like that then we should give up 
now.

You don't think margins' results are immune to criticism do you? Without
an autofill option or something I doubt margins as a proposal could
even get off the ground.

> >> There are also some cases where truncation
> >> could be related to strategic behaviour but in
> large real
> >> life elections this is hopefully marginal and
> mostly not
> >> rational.
> > 
> > Highly unlikely if "strategic behavior" includes not
> voting for the
> > worse of two frontrunners. That is a defensive
> strategy, so if you're
> > not including that I'm not sure what you mean.
> 
> There may well be many voters that truncate candidates that
> they consider to be strong competitors of their favourites.
> I noted already above that such behaviour may easily ruin
> the good properties of Condorcet methods. 

"Such behavior" could, yes... Strategically *incorrectly* truncating too
high could ruin it. But in general, in itself, truncating the worse of two
frontrunners doesn't hurt anything.

> I hope that this
> behaviour would be marginal and I also think that it is
> luckily in most cases irrational. On the other hand I'm sure
> that we can not fully get rid of it. (I was planning to
> reply something to Forrest Simmons on this topic. Maybe
> soon. One key point is that if people don't rank the
> moderate candidates (plausible winners) of the competing
> sections then the more radical ones may easily win. That
> would ruin one key idea of the Condorcet methods and could
> even lead to their failure after being implemented in some
> society.)

This is why I like mechanisms related to antiplurality. You don't ask
the voters (without any guarantees) who their second-favorite is, you
ask them who they want to see lose.

Kevin Venzke