[EM] Defensive strategy for Condorcet methods

[Juho Laatu]

On 9.6.2011, at 1.31, Kevin Venzke wrote:

> 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.

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?

> 
> 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?

> , 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?

> 
> 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...?


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)?

Juho



> , to avoid the
> problem. (You still can't use Borda.)
> 
> Kevin Venzke
> 
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