[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 :
> 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.

In my recent simulations, when some voters saw the advantage of using
burial strategy, 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.

So I expect that methods with greater burial incentive will just have
more (voted) majority favorites, and candidate withdrawals, to avoid the
problem. (You still can't use Borda.)

Kevin Venzke