[EM] Condorcet How? JL

[Juho]

On Apr 14, 2010, at 7:07 AM, Kevin Venzke wrote:

> Hi Juho,
>
> --- En date de : Mar 13.4.10, Juho <juho4880 at yahoo.co.uk> a écrit :
>>>> This time the
>>>> election will be arranged using WV. B supporters
>> note that
>>>> they can win by not supporting C any more. C
>> supporters do
>>>> not have the same incentive since they are about
>> to win.
>>>
>>> That's only true if C voters behave on autopilot and
>> don't consider
>>> the specific election they're voting in. Otherwise
>> they have exactly
>>> the same incentive.
>>
>> In the example I assumed that polls tell clearly that C is
>> more popular than B.
>
> I'm basically saying it doesn't seem to make sense that some B  
> voters are
> untrustworthy but all C voters are trustworthy and think B voters are
> also.
>
> Anyway I don't find this scenario compelling because while you dislike
> that B voters can steal the election, you have no way of knowing that
> that's what they are doing. You're going to punish everybody just to  
> be
> safe.
>
> In any scenario like this, some B voters will say that they honestly
> did not like C.

- My assumption was that in competitive political elections all voters  
may be untrustworthy if they have some easy strategy available
- It doesn't really matter whether or not B voters will tell what they  
did (the problem is that they had an easy strategy available)

>
>>> Maybe this is later in your mail, but I still don't
>> understand what you
>>> mean by performance with sincere votes.
>>
>> Simply, given sincere opinions and votes that reflect those
>> opinions, does the method elect the best possible
>> winner(s).
>>
>>> The fact that you don't present
>>> any scenarios about this
>>
>> I think I did. For example sincere 49: A>B, 49: C>D,
>> 1: D>B could be one such example. WV elects D, and that
>> could be considered less than perfect performance with
>> sincere votes.
>>
>> (I however think that different elections may have
>> different targets and therefore the best winner could be
>> different in different environments. For example the method
>> might put emphasis on finding a winner that all like a lot
>> on average, that is strong or that is not too much disliked
>> by any.)
>
> I think you have a party list mentality. It seems like you want to  
> find
> a winning faction, here, and pick the winner within that faction. You
> see the D vote and count it to {CD}. But that's an bad idea if you're
> trying to pick the candidate more representative of *all* the voters.

I don't think I wanted them to feel this way. I just assumed that in  
these elections there was a clear division between "left" and  
"right" (sincere in this example) (truncation would probably not be as  
heavy in typical real life elections, but this example was just a  
simplified example to show that WV decisions with sincere votes may  
not always be what one would want them to be).

>
>>> makes me believe that you consider all
>>> truncation a strategy that would be eliminated by
>> margins,
>>
>> Definitely I don't believe that margins would be free of
>> strategic temptations, and I don't think "elimination of
>> truncation" is any key target in margins. And in some sets
>> of votes margins may be worse than in WV. But margins is
>> somewhat more appealing to me with sincere votes. Also
>> (contrary to what one often hears) I don't believe that WV
>> would be mostly superior in the strategic scenarios.
>
> I think it would, because a majority can truncate in an intuitive way
> and gain a favorite betrayal guarantee; i.e. they can rank their  
> preferred
> candidates however they want without making the candidate they're  
> united
> behind lose.
>
> Is margins better at defection scenarios? Only if it works. And I  
> don't
> think that's realistic.

There are strategic scenarios where margins is worse (and vice versa).  
Since I hope that Condorcet elections will generally allow sincere  
voting I put considerable weight also on how the method performs with  
sincere votes.

>
>> The
>> benefits of margins are maybe on its "naturalness" and in
>> the fact that despite of not being tailored for strategic
>> situations it nevertheless works quite well also in
>> strategic environments (maybe partly thanks to not being
>> fiddled in any way).
>
> Not sure why you think this, but ok.
>
>>> and so
>>> therefore a scenario with sincere votes would be
>> resolved exactly the
>>> same between WV and margins.
>>
>> I didn't get this. Do you maybe mean that sincere votes
>> would be always fully ranked? (This would explain why you
>> didn't find any sincere scenarios among the WV examples that
>> I listed.)
>
> I think I first asked this question before seeing your scenarios.
>
> My claim here was that *you* probably believe that sincere votes would
> always be fully ranked, which would be evidence of badness by WV every
> time some ballots don't fully rank.
>
> If you thought that, and you claim you don't, then it wouldn't be  
> possible
> to show WV giving a bad result with sincere votes, because with  
> sincere
> votes there would be no distinction between the two methods.
>
>>> The only other thing I can think of is that you are
>> concerned about WV's
>>> treatment of people who actually want to abstain from
>> a contest and
>>> be counted as a schizophrenic in the margins style. In
>> that case I suggest
>>> that those WV voters flip a coin to simulate the
>> margins treatment of
>>> their vote.
>>
>> That'd make margins and WV identical and we would not even
>> have to name which one of these approaches to measure
>> preference strength we are using.
>
> Only with those ballots which did that.
>
>> I try not to assume
>> anything special on why some voters rank some candidates
>> equal (truncating at the end or otherwise tied elsewhere).
>> Technically the methods treat all reasons to rank some
>> candidates equal the same way (be it strategy, laziness to
>> rank all candidates, sincere opinion that the candidates are
>> equal, opinion that the candidates are close enough to equal
>> to rank them equal, or equality because the voter simply
>> does not know anything at all about those equally ranked
>> candidates). The explanation of the vote set may assume
>> something about why people voted the way they did but the
>> method can not (unless it contains some guidance to the
>> voters on how the method / organizers expect voters to vote
>> when they have certain feelings).
>
> But when you "try not to assume anything special on why some voters  
> rank
> some candidates equal (truncating at the end or otherwise tied  
> elsewhere)"
> this leaves you no justification for your particular treatment of tied
> rankings. It is not obvious to split one voter, make him vote against
> himself, and *count* that to defeat strength (which is the point of  
> all
> of this).
>
> Of course, that is the explanation from the WV perspective.  
> Alternatively
> you're just subtracting the vote totals. Ok, why *subtract*? Why would
> the strength be based on the absolute difference of the vote totals?  
> It
> should be the ratio surely. If you claim to not care about  
> abstentions from
> a contest, then a 5:1 ratio should always be stronger than 4:1.
>
> What is the "naturalness" of margins?
>
> It's not even as easy to solve.

Yes, there could be such variants. I addressed this option shortly in  
my first reply to Robert Bristow-Johnson in this chain.

>
>>>>> I don't understand the distinction you are
>> making.
>>>>
>>>> What I'm after is one stable explanation why the
>> voters
>>>> felt and voted as they did. If there are multiple
>> possible
>>>> explanations then I like to analyze them one by
>> one. The
>>>> situation that I try to avoid is one where one
>> feature of
>>>> the scenario will be explained using one kind of
>>>> explanation/arguments (e.g. lack of information on
>> the
>>>> strength of C)
>>>
>>> I would say this is more key
>>>
>>>> and another one with another explanation
>>>> (e.g. interest not to allow third parties grow).
>>>
>>> I can't believe I need to propose that a major party
>> doesn't want to help
>>> another party to grow? One going after the same votes
>> even.
>>
>> Yes, parties are typically competitive and want to "steal"
>> the votes of the others. If there is a special historical
>> relation between two established parties and new ones that
>> have earlier been unable to win and that might suffer also
>> now because of that legacy, this could be mentioned in the
>> explanation.
>
> No there is no special relation, there is the typical relation that  
> you
> just mentioned.
>
>>>> My text was not very good. The basic scenario that
>> I don't
>>>> like is one where multiple groups rank only the
>> candidates
>>>> of their own favourite group. The votes could be
>> 100:
>>>> A1>A2>A3, 100: B1>B2>B3, 100:
>> C1>C2>C3
>>>> etc. WV seems to think that all candidates are
>> about equal
>>>> (with these votes that are at least close to
>> sincere) since
>>>> any additional (strategic or sincere) vote may
>> make any of
>>>> these candidates win. WV thus seems to ignore the
>> sincere
>>>> unanimous opinions/rankings within each group, and
>> one could
>>>> say that WV doesn't measure the opinions as one
>> would
>>>> expect.
>>>
>>> I assume if you add 1 A3 vote, margins elects A1. That
>> strikes me as
>>> illogical unless you're voting a party list method or
>> something. At
>>> least in WV you can say that A3 might be the approval
>> winner.
>>
>> Before the last vote A1, B1 and C1 were tied in margins.
>> Margins will not allow any other candidates win without a
>> considerable number of new votes. That last vote didn't
>> support A1 but it made the situation of B1 and C1 slightly
>> worse. They now lose to a candidate that loses a lot to A1
>> while earlier they didn't lose to any of the candidates.
>> That difference is not big but who else should be elected if
>> not A1? Also WV gives victory to A1 in this example (if the
>> additional vote was "1: A3" and not e.g. "1: A3>C2").
>
> Ok I see. A3 has no claim over A1 just from the bullet vote. So assume
> it's A3>C2. In that case according to your analysis, the A candidates
> collectively beat B and C,

Only A3 beats the B and C candidates, not all A candidates, no  
"collective" beating.

> and then "privately" decide almost unanimously
> that A1 is the candidate who should win, even though Team A wouldn't  
> have
> won without the vote that didn't like A1 at all.

Yes, that last vote did not support A1 at all, but it was the last  
straw that broke the back of B1 and C1 in margins when it made them  
lose to one of the candidates (A3).

>
> Yeah I don't like that. I'm trying to pick the most median-like  
> candidate,
> not pick a party and then have an internal election.

All voters were free to take position on which one of the A candidates  
was best. Many found them equal (or equal enough not to bother to rank  
them). In a real life election B and C supporters could well agree  
with this ranking. There was nothing "internal" except the common  
pattern of voters truncating candidates that they do not support.


(I note that I have used term win in a sloppy way. All Condorcet  
methods do not necessarily decide always the same way. I just referred  
to some expected decision based on the strength of WV and margins  
comparisons.)

>
>>>>> Fundamentally we're trying to rank defeat
>> strengths,
>>>> not decide how to
>>>>> split up votes. The WV mentality is that the
>> more
>>>> people that participate,
>>>>> the better that information is.
>>>>
>>>> Note that vote A>B=C may sometimes mean that
>> this voter
>>>> didn't want to participate in the B vs. C
>> question, but it
>>>> may as well be a clear statement that B=C.
>> Non-participation
>>>> may also mean that the voter wants other voters to
>> decide
>>>> without him/her. If we don't collect separately
>> information
>>>> on what the reason behind the equal rankings is we
>> can not
>>>> assume one way or another.
>>>
>>> I wouldn't object so strongly to a method which
>> counted explicitly equal
>>> rankings according to margins (even though this is
>> strategically
>>> pointless) but truncated rankings according to WV.
>>
>> Does word "truncation" carry a meaning here? (other than
>> the technical property of equal ranking of the last
>> candidates) (e.g. "ranked equal last since not approved",
>> "using ballots where unranked last do not have any markings,
>> so they can be considered not approved", "not ranked since
>> it was too tedious to rank them")
>
> For me truncation means "did not evaluate because they were not good
> enough." But "good enough" could be determined according to the  
> voter's
> expectation for the election.
>
>>> I should split it into two statements perhaps:
>>> 1. when people are truncating then your defensive
>> strategy in margins
>>> should be to vote for the best frontrunner, because
>> margins won't
>>> guarantee that a literal majority can get their way by
>> just voting
>>> sincerely for the better frontrunner and everyone
>> thought to be better.
>>
>> I hope that in large public elections people never have to
>> resort to defensive strategies. If people start to use
>> defensive strategies widely in any large public Condorcet
>> elections then I consider that to be a failure of the
>> method. I.e. the best promise of Condorcet is that it would
>> allow sincere voting. Strategic Condorcet would not be nice.
>
> I don't think Condorcet can do that, and I don't think it matters.  
> There
> isn't enough benefit:risk to trying to get complete rankings.

I'm ok with "sincere opinion", "don't care" and limited "lazy"  
truncation. Only strategic use truncation ("attack" or "defence") is  
something I'd like to live without (or keep it marginal). (Also  
excessive "lazy" truncation (e.g. widespread "lazy" bullet voting)  
would be bad.)

>
>> And strategic defensive truncation is not nice if widely
>> spread. That means also going towards plurality / bullet
>> voting.
>
> Strategic defensive order-reversal is also not nice, and it will  
> lead to
> plurality, at least in its results.

Yes, order reversal is also not nice.

>
> Using defensive strategy in both WV and margins is a good idea in  
> general,
> even with no knowledge of plans for offensive strategy. In WV it makes
> offensive strategy unlikely to be reliable, and in margins it can  
> protect
> a majority you are part of.

Widespread strategic voting could destroy the otherwise good  
properties of Condorcet methods. I'd like to avoid also the use  
defensive strategies.

>
>> I'm not sure if semi-controlled truncation where
>> some voters are expected to truncate (e.g. the ones that
>> expect to be the victims of a burial attack, or those who
>> think they are leading) while some others are expected to
>> vote sincerely is much nicer. And as already noted, there
>> may be disagreements and misunderstanding on who is supposed
>> and/or allowed to truncate. This approach might lead to a
>> big mess.
>
> If you're talking about scenarios where one fragment of a faction is
> tasked with doing one particular thing in order to steal an  
> election, yes,
> I'm pretty sure that's a bad thing

Also defensive strategies may ruin the election (e.g. if the left wing  
supporters truncate the candidates of each others).

> , but no, I don't think it is a very
> likely concern. And the only the fact that you're specifically talking
> about truncation would make this concern favor margins over WV. I  
> don't
> remember any reason to think that margins is harder to compromise than
> WV.
>
>>> I should have answered above what this means. I assume
>> at this point
>>> that you have an idealized view of what would happen
>> when nobody ever
>>> truncated.
>>
>> I believe yes :-). I try to see Condorcet methods as a
>> group that in a suitable environment (very competitive but
>> not pathologically/irrationally competitive and not beyond
>> repair) would allow sincere voting as the main rule for all
>> rational voters.
>
> Ok. We will have to disagree on that.

Ok, it seems I have more trust on votes staying reasonably sincere.  
Condorcet methods might still be a good option in societies that can  
not refrain from widespread strategic voting. What I'm afraid in WV is  
that in such strategic environments the truncation based strategic  
opportunities, the truncation based defensive strategy, lazy  
truncation and messages like "truncated candidate = not approved  
candidate" (that may lead to truncation of the main competitors) could  
together lead to lots of truncation (and related problems like the  
Burr dilemma).

Juho


>
> Kevin Venzke
>
>
>
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