[EM] Defensive strategy for Condorcet methods

[Kevin Venzke]

Hi Juho,

--- En date de : Mer 8.6.11, Juho Laatu <juho4880 at yahoo.co.uk> a écrit :
> > --- En date de : Mer 8.6.11, Juho Laatu <juho4880 at yahoo.co.uk>
> a écrit :
> >> There has been quite a lot of
> >> discussion around the strategic vulnerabilities of
> Condorcet
> >> methods on this list recently. In general I think
> Condorcet
> >> methods are one of the least vulnerable to
> strategies, and
> >> in most typical elections their vanilla versions
> are simply
> >> good enough. In the case that people would start
> voting
> >> strategically there is one interesting defensive
> strategy
> >> that has not been discussed very much. The
> defensive
> >> strategy is to not tell your sincere opinions in
> the polls.
> >> Most Condorcet strategies are based on quite
> accurate
> >> understanding on how others are going to vote. If
> I expect
> >> someone to play foul play, I might just refuse to
> give the
> >> required information to them, and recommend others
> to do the
> >> same. (Also giving planned false information to
> mislead the
> >> strategists is possible, but more difficult.)
> >> 
> >> This approach does not work about irrational
> voters that
> >> will bury anyway, just in case that might help.
> But the
> >> point is that in Condorcet elections the best
> strategy, in
> >> the absence of good information on the
> preferences, is to
> >> vote sincerely. In real life this strategy could
> be
> >> mentioned as a possibility in the case that
> strategic voting
> >> becomes threatening. The outcome hopefully is such
> that all
> >> parties, experts and media would recommend voters
> to vote
> >> sincerely and not try strategies. That would be
> better to
> >> all than having to live without the interesting
> polls. What
> >> do you think? Is this a way to drive away possible
> evil
> >> spirits and strategy promoting parties, experts
> and media?
> > 
> > I don't see this working because you will never be
> able to disguise who
> > the frontrunners are.
> 
> I agree that there is always some information on the
> popularity of different candidates (also without any polls).
> But does this mean that it would be a working strategy
> (=likely to bring more benefits than harm) e.g. to always
> bury one of the assumed frontrunners under one of the
> assumer non-frontrunners? Is there some well known strategy
> that would work in this situation?

No, I wouldn't say that. I do think there are methods that offer two
bad options and one of them is burial, though.

> > 
> > In my recent simulations, when some voters saw the
> advantage of using
> > burial strategy
> 
> Was this decision ("saw the advantage") based on highly
> inaccurate information like being able to guess who the
> frontrunners might be?

What? The voters are participating in repeated polling, and have the
ability to see not just each poll's outcome but what they could have
accomplished by doing anything else. Buriers see that burial is an
advantage if the opposing side is sincere. When pawn-supporting voters
compromise, the buriers have no reason to revert to sincerity. (They
don't even know what sincerity is.)

If what you're asking is whether this could be thwarted by not revealing
any polls to the voters, then I can't address that. My voters have to
have polls in order to learn how the method works.

> > , the defensive strategy used in response seems to be
> > compromise strategy, as opposed to truncation or
> burial-in-turn, things
> > that risk ruining the result.
> > 
> > That is, there are voters who know they can't expect
> to gain anything
> > by voting sincerely, so they play it safe.
> 
> I agree that there are situations where some voters will
> not lose anything by using whatever strategy with even some
> infinitesimal hope of improving the outcome (e.g. when they
> know that otherwise the worst alternative will win). But how
> can they know (based on the limited available information)
> that sincere voting will not help them? Do they know for
> certain that some strategy is more likely to help (and not
> harm) them?

I'm talking about voting for a sincere favorite who is not believed to
be a contender. If that candidate can't win, and could be a liability,
then you could logically decide to dump him.

> > So I expect that methods with greater burial incentive
> will just have
> > more (voted) majority favorites
> 
> I didn't quite get this expression. Would this be bullet
> voting by majority or what?
> 
> > , and candidate withdrawals
> 
> Does this mean having only few candidates or ability to
> withdraw after the election and thereby influence the
> counting process or...?

What I'm saying is that methods with greater burial incentive will
probably see supporters of pawn candidates stop voting for those
candidates, and those pawn candidates would probably drop out of the race
more often. (I think that compromise incentive and nomination 
disincentive go hand-in-hand.)

This is as opposed to the theory that methods with great burial incentive
will see a larger number of train wreck outcomes as voters play chicken
with each other.

> I didn't quite catch what the impact of this to the
> usefulness of the reduced poll information based defensive
> strategy would be. Could you clarify. Did you say that
> already very rough information on which candidates are the
> frontrunners would give sufficient information to the
> strategists to cast a working (=likely to bring more
> benefits than harm) strategic vote (in Condorcet methods in
> general or in some of them)?

The relevance is more to the question of defensive strategy under
Condorcet methods, than to your proposal.

I do believe that rough information on the frontrunners is enough to
tell you *who* to bury, if you were going to, and also who might
consider compromising to avoid a risk.

I am mostly concerned about burial in methods that seem to encourage it
without voters even having a specific plan.

Kevin Venzke