[EM] Defensive strategy for Condorcet methods

[Kevin Venzke]

Hi Juho,

I have to trim this due to being short on time.

--- En date de : Mar 14.6.11, Juho Laatu <juho4880 at yahoo.co.uk> a écrit :
> >>> If
> >>> the answer is no or almost never, and I'm the
> only
> >> nutty voter that wants
> >>> to vote A>C>B, lose nothing, maybe gain,
> with
> >> everyone else voting
> >>> sincerely, there's no harm done, right?
> >> 
> >> Except that you are encouraging also others to do
> similar
> >> tricks. One day they might do so.
> > 
> > Well, then I would stop.
> 
> Maybe already earlier?

I wouldn't stop until I know there's risk of a problem, I think.

> > Interesting question though, whether we could show
> mathematically (or
> > experimentally) that I as voter definitely would
> prefer to keep the 
> > method from becoming broken, assuming I actually have
> some influence on
> > that.
> 
> You might tell the strategists that you will give false
> information in the polls in order to make their strategic
> attempts fail. I also believe there are various norms of
> acceptable behaviour in the society. Probably you don't brag
> to others if you have stolen candy from kids. In the same
> way your neigbours might not like you if you would regularly
> brag about trying to cheat in the elections.

But if there were some law that, as a side-effect, required me to
steal candy from kids, I would have to do that, and I don't think my
peers would be willing to judge me.

> >> In margins (and maybe in other variants too) ties
> should
> >> not carry any other additional meaning but that
> the voter
> >> didn't support X>Y nor Y>X.
> > 
> > In a general context it is really unclear to me what
> this means. It's
> > like an IRV-oriented criterion that assumes you're
> doing eliminations.
> > It may be completely possible to satisfy you on this
> point, and also 
> > have a method that I don't find irritating. From what
> you've literally
> > written here I don't even see how it excludes WV.
> 
> There are maybe two ways to understand what the election
> methods do. 1) Elect the candidate that is best according to
> some (sincere) philosophy based on the given (hopefully)
> sincere opinions of the voters. 2) Generate a set of
> (whatever kind of) rules and let the voters cast their votes
> in the best way they can to make the outcome best possible
> for themselves. In the first approach we should have an
> interpretation on what ranking two candidates equal means
> from the utility and sincere preference point of view. If
> the intended meaning of equal ranking is the same as
> flipping a coin (and often it is about the same), then also
> the results should be the same (in the first
> interpretation). In the second interpretation any rules are
> ok as long as other stated requirements are met (e.g. equal
> treatment of all voters).
> 
> WV is not excluded even in the first interpretation if
> there is a good explanation (that corresponds to some
> "sincere" philosophy) to why pairwise defeat strengths are
> measured the way WV does. It is quite natural to say that
> the number of voters on the opposing side is an important
> criterion (but may leave open the question does the number
> of voters in favour of that candidate have some meaning as
> well). I think the margins (sincere) philosophy is easier to
> explain than the WV philosophy.

But with the first approach, with people being sincere, you shouldn't
have to worry about equal ranking or truncation for the most part. Then
WV and margins are the same.

> > How about a method where, if there is a cycle, we take
> the top three
> > FPP candidates (call them ABC in descending order). C
> wins if and only
> > if he gets 75%+ top-two rankings (i.e. A>C B>C
> C>?). Otherwise we will
> > elect whichever of A and B has the most ballots in the
> form A>C or B>C
> > respectively. Fun I think?
> 
> These methods were already discussed in other mails. I just
> note that if A>C means that A supporters should rank C
> second in order to increase their chances to win in case of
> a top cycle, then things get quite tricky. Burial
> strategists probably ranked C second, and that could
> increase their chances of fooling the system.

Yes, the idea is that you need to vote for C to win, but if too many
people do it then C wins. I'm just trying to make it as explicit as
possible, in order to ask whether this method is still good enough to
use.

Kevin Venzke