[EM] Defensive strategy for Condorcet methods

Dave Ketchum davek at clarityconnect.com
Thu Jun 9 19:37:12 PDT 2011


Seems that some are so lacking in understanding Condorcet that they  
fear it.  So, a couple basics:
.  The voter can rank such as A=B=C, saying exactly equal approval of  
these three over all other candidates.  This has the same effect as it  
would have in true Approval.
.  The voter can rank such as A>B>C, approving these three over all  
other candidates.  Here the ranking reads as A>B, A>C, and B>C for  
detailed liking among those ranked..

On Jun 9, 2011, at 8:04 PM, Kevin Venzke wrote:

> Hi Juho,
>
> --- En date de : Jeu 9.6.11, Juho Laatu <juho4880 at yahoo.co.uk> a  
> écrit :
>>> No, I wouldn't say that. I do think there are methods
>> that offer two
>>> bad options and one of them is burial, though.
>>
>> (There is no working strategy, but there are some
>> options??)
>
> Absolutely. I'm being honest when I say I don't know how I would vote
> in the simplest election. If all I know is that my preference order is
> A>B>C and the frontrunners are A and B, what should I do? Let's go  
> over
> it.
>
> 1. Vote sincerely, A>B>C. On a gut level I *don't want* to do this. B
> is the candidate I am trying to beat. Why do I want to help him beat  
> C?
> This can actually help B and it will never help A. I feel like a  
> sucker
> if I expose myself to this risk for no possible benefit. I do not need
> to know whether there is *really* a threat; it makes no sense for me.

You are saying that you are not sure you really voted what you  
thought.  Your words imply A>C would be truer sincerity - even A>C>B  
would be nicer to B than he deserves - leaving B unranked would place  
him equal to all others you leave unranked.
>
>
> 2. Lie, and vote A>C>B. Now I'm a bad guy who you think must have some
> strategy in mind for picking this manner of voting. If I thought B  
> voters
> were going to use this same strategy against me then in voting like
> this I might just be defending myself. But outside of that  
> possibility,
> maybe I just don't have any good options?
>
> 3. Bullet-vote for A. Nope, not if this is margins. That's just  
> splitting
> the difference or flipping a coin. It's childish to vote like this.
> But actually, I think I might vote this way, just because I wouldn't  
> have
> to feel like either a sucker or a jerk for doing it.

Depends on what you think of C.  Above you were helping C as second  
choice after A; here you would demote C to unranked.
>
>>> 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.)
>>
>> You seem to assume repeated polling, sufficiently accurate
>> results, unchanging results, similar results from all the
>> polling companies, no intentionally misleading polls, no
>> meaningful changes in behviour before the election day, no
>> interest to give false information in the polls, maybe no
>> impact of planned strategies on the voting behaviour of
>> others, good enough control of the strategists (if needed).
>
> Your description isn't that unfair. Changes are possible, but most  
> methods
> and scenarios become pretty stable.
>
> I am skeptical about the concept of intentionally misleading polls,
> especially when the polling doesn't work as predictably as in FPP,  
> where
> the belief that candidate X is strong is generally going to help X.
>
> I don't really believe in "planned strategies" that are kept secret.  
> If
> this is really a problem, then, ok, my simulations aren't covering  
> this.
>
>>> 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.
>>
>> In some methods like Approval poll information is needed to
>> cast a vote in line with the typical recommendations on how
>> to vote (= approve one of the frontrunners etc.). One could
>> also have Approval elections without such information. In
>> that case voters would not vote strategically but would
>> maybe mark those candidates that they approve for the job.
>>
>> In Condorcet the basic assumption is however that voters
>> can sincerely rank the candidates. Doing so tends to improve
>> the outcome of the election. The strategy of making polls
>> unreliable may thus improve the outcome of the election.
>
> Yes, if you can make polling unreliable, it would be very irritating
> when the election method is Approval or FPP, and it might help  
> Condorcet.
>
>>>> , 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.
>>
>> Ok, with favourite candidates that have no chance of
>> winning one can usually do pretty much whatever one wants.
>> That typically does not make the results of this election
>> better nor worse.
>
> It should also be a *design goal* that this does not make the  
> results of
> the election better or worse.

"whatever one wants" is true for such a favorite.  You still have a  
chance to affect who wins.
>
>
>> Often it makes however sense to make the
>> result as favourable to this favourite candidate as possible
>> since there are also secondary targets like helping this
>> candidate win in the next elections or just showing how much
>> support this line of thinking has among the electorate.
>
> Yes, it's possible. I don't see a way to incorporate that  
> experimentally.

This is polling class data for such secondary targets.
>
>
>>>>> 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.)
>>
>> Ok, if there were such threats.
>
> Hopefully from my first comments of this mail it's clearer what kind  
> of
> threat I have in mind.
>
>>> 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.
>>
>> Note that I proposed a preemptive defensive strategy to be
>> applied instead of concrete ones. I don't really like the
>> idea that people would start falsifying their preferences in
>> the actual election in order to defend against actual or
>> imagined strategic threats.
>
> Haha. Every method has this problem to some extent, nothing to do with
> burial even.
>
>> Truncation is one typical
>> strategic defence in some Condorcet methods. I prefer poll
>> level preemptive defence to this since that way we can avoid
>> e.g. Condorcet becoming "more plurality like".
>
> If it works, sure, but if it doesn't, I would guess margins is the
> "more plurality like" in the sense that the winner's first preference
> count will probably be greater.

Truncation is often useful, apart from possibly being called a defense.

Dave Ketchum
>
>>> I do believe that rough information on the
>> frontrunners is enough to
>>> tell you *who* to bury, if you were going to
>>
>> Yes, there is no point in burying anyone else but those
>> that are ahead of one's own favourite. The information on
>> which candidates are about to beat one's favourite should
>> however be correct with good probability.
>
> I hope we are fortunate enough to have such a concern.
>
>>> , and also who might
>>> consider compromising to avoid a risk.
>>
>> I'm afraid this information is already quite difficult to
>> collect and may not be very accurate and reliable.
>
> This refers to the supporters of pawn candidates, so to my mind it is
> almost just the inverse of who are the frontrunners.
>
>>> I am mostly concerned about burial in methods that
>> seem to encourage it
>>> without voters even having a specific plan.
>>
>> I wonder where the accurate line goes on which Condorcet
>> methods are vulnerable to burial and which ones are not :-).
>
> I do not know, but I have an interest in the question.
>
>> I'm afraid that in Condorcet methods there might be many
>> voters that rank their worst competitor last in the (not
>> very well founded) hope of improving the results from their
>> point of view :-).
>>
>> More seriously, maybe some concrete written rules to voters
>> on how to bury in Condorcet elections (on in some Condorcet
>> version) would demonstrate that poll information can indeed
>> be efficiently used by regular voters in some real
>> elections. I tend to think that in many environments burial
>> would not be a problem, and in line with this mail thread,
>> maybe one could simply weaken the available poll information
>> and education of the voters if strategies start appearing.
>
> If the nature of burial is that nobody thinks to do it without some  
> kind
> of plan, then I am not nearly as worried about it. But since I myself
> am not sure what I ought to do when I "can't" use defensive truncation
> anymore, I am concerned.
>
> Kevin Venzke





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