[EM] (3) MJ -- The easiest method to 'tolerate'
C.Benham
cbenham at adam.com.au
Wed Sep 7 14:18:21 PDT 2016
On 9/8/2016 5:01 AM, Jameson Quinn wrote:
> I am completely baffled by the idea that IBIFA is less complicated
> than U/P.
C: I never said that it was. I just said that U/P is "quite
complicated", meaning that it is a lot more complicated than Approval
(and more complicated than MTA). Its extra complexity over
those methods doesn't seem to buy much.
if you include in U/P 's explanation all the palaver about the default
ratings it becomes quite long and complex. 3-slot IBIFA can be defined
fairly succinctly, but I'm
not sure how well the "man in the street" would understand it.
> I also don't agree that .. U/P "nearly always simply elects the
> Approval winner".
C: Again, I'd be interested in seeing a plausible example of when it
doesn't.
> Condorcet versus Majority Condorcet: I do not believe in the concept
> of "irrelevant ballots", or that we should "simplify" a scenario by
> removing a balanced set of ballots.
C: Why not?
> Dominant in top-ratings: taking this as a strong argument for who the
> correct winner is, is inherently subject to clone effects
C: I never used the phrase "dominant in top-ratings". These are
supposed to be ratings (instead of simply rankings). In that case clones
are technically supposed to be rated the same.
At one point I said that C would be "positionally dominant" if all C's
supporters truncated, meaning C would have both the highest Top Rating
score and the highest Approval score.
> After all, as long as we're making up arbitrary scenarios, we can
> arbitrarily assume that the 3 A voters are in fact attempting strategy.
C: No, you have to be able to justify the result on the assumption that
all the votes are sincere, or at least are all equally likely to be
sincere. Otherwise you'd be able to argue
that in this or that scenario the most ridiculous method "gave the best
result".
Chris Benham
> Once again, I'm going to stand behind my view that U/P is a better
> practical reform proposal than IBIFA, and that there are cases where
> U/P gets the right answer and IBIFA doesn't. But once again, I'm going
> to preface it by saying I think IBIFA is a great method overall.
>
> So. Remaining debates.
>
> Condorcet versus Majority Condorcet: I do not believe in the concept
> of "irrelevant ballots", or that we should "simplify" a scenario by
> removing a balanced set of ballots.
>
> Dominant in top-ratings: taking this as a strong argument for who the
> correct winner is, is inherently subject to clone effects. My
> "unserious" example was a (serious) attempt to show this.
>
> "It seems that you want a quite complicated method with a nearly as
> strong as possible truncation incentive and that nearly always
> simply elects the Approval winner (while somehow "tending to respect"
> majority Condorcet without actually meeting the Majority
> Condorcet criterion)."
>
> I am completely baffled by the idea that IBIFA is less complicated
> than U/P. If you want to, we can each post a 3-minute video where we
> explain our method to a random "person on the street" and then ask the
> person to explain it back to us. I'll bet that this would show U/P as
> far simpler to understand. If you agree, I'll let you set any
> reasonable procedure for each choosing our subject/explainee.
>
> I also don't agree that the U/P has a "nearly as strong as possible
> truncation incentive" or "nearly always simply elects the approval
> winner".
> On the first point: I think that in a chicken dilemma situation, U/P
> would lead to less truncation than many other methods, including
> things like MCA or MJ, because in U/P, chicken truncation is only
> helpful precisely insofar as it's risky. On the second: I think that
> there is a not-insignificant subset of voters who strongly want to
> cast a ballot that's expressive enough to distinguish their favorite
> from their preferred frontrunner. In approval, such people would
> bullet vote; in U/P, they could still rate the compromise frontrunner
> as acceptable. This could easily lead to different (and better) outcomes.
>
> 2016-09-07 15:01 GMT-04:00 C.Benham <cbenham at adam.com.au
> <mailto:cbenham at adam.com.au>>:
>
> On 9/7/2016 10:15 PM, Jameson Quinn wrote:
>
>> C: C is the clearly voted Condorcet winner
>>
>> But not the majority Condorcet winner. I regard majority
>> Condorcet as something any good voting system should tend to
>> respect, but non-majority Condorcet as only a weak signal.
>>
>
> C: The Majority Condorcet winner is always the Condorcet winner.
> It is ridiculous to suggest that failing to elect a Condorcet
> winner is a step in the
> direction of "tending to respect the majority Condorcet winner".
>
> The "Majority Condorcet" concept is vulnerable to Irrelevant
> Ballots, and to put it forward as some especially desirable
> criterion is nonsensical.
>
> In our example, would removing 3 plumping ballots from each of the
> candidates really turn C into a stronger candidate? Because the
> effect would
> be to change C from a mere Condorcet winner (who you say should
> lose to the approval winner) into a fabulous Majority Condorcet
> winner (who you
> say the method should "tend" to respect).
>
> (The only point of the criterion is that some methods happen to be
> able to meet it, but not the normal Condorcet criterion.)
>
> 20: A>B
> 25: B>A
> 20: C>B
> 26: C
>
> 91 ballots. Majority threshold = 46.
>
> C > B 46-45, C > A 46-45.
>
> Or of course the question can be posed the other way: does giving
> each candidate 3 extra plumping ballots really make C a weaker
> candidate?
>
>> Whoops... I'm sorry. Those were the averages over a large number
>> of polls, but then a week before the election, A had a heart
>> attack. The actual scores, with 3 ballots still to count from A's
>> former stronghold precinct, are:
>>
>> 48: B
>> 49: C
>>
>> I guess C wasn't so dominant in top-ratings after all. Once we
>> count those last three ballots, we'll have a clear winner here,
>> and there's every chance it could be B.
>
> C:I take it this is Jameson not being serious (and perhaps trying
> to shift goal-posts).
>
> One of IBIFA's obvious advantages over "U/P" and MJ and the
> other Bucklin methods is that it has a
> much weaker truncation incentive. In the example (with 100
> ballots) U/P penalised the 20 C>B voters
> for not truncating. Had they done so C would have won.
> (Unsurprising, since that would have made C positionally
> dominant as well the Condorcet winner).
>
> It seems that you want a quite complicated method with a nearly as
> strong as possible truncation incentive and that nearly always
> simply elects the Approval winner (while somehow "tending to
> respect" majority Condorcet without actually meeting the Majority
> Condorcet criterion).
>
> BTW, I'd be mildly interested in seeing one or two of your
> realistic examples where U/P doesn't elect the Approval winner.
>
> Given from what I can make of your method goals, why don't you
> simply propose Majority Condorcet//Approval ?
>
> Chris Benham
>
>>
>>
>> 2016-09-07 8:17 GMT-04:00 C.Benham <cbenham at adam.com.au
>> <mailto:cbenham at adam.com.au>>:
>>
>>
>> 3: A
>> 20: A>B
>> 25: B>A
>> 3: B
>> 20: C>B
>> 29: C
>>
>> C > B 49-48, C > A 49-48, B > A 48-23.
>>
>> Top Ratings scores: C 49, B 28, A 23
>>
>> Approval scores: B 68, C 49, A 48.
>>
>> On 9/7/2016 7:09 AM, Jameson Quinn wrote:
>>> IBIFA elects C. U/P elects B. It's clear to me that B is
>>> better. The 3 A-only voters are likely attempting a chicken
>>> strategy.
>>
>> C: C is the clearly voted Condorcet winner
>>
>>
>> But not the majority Condorcet winner. I regard majority
>> Condorcet as something any good voting system should tend to
>> respect, but non-majority Condorcet as only a weak signal.
>>
>> and by far the most top-rated candidate.
>>
>>
>> Whoops... I'm sorry. Those were the averages over a large number
>> of polls, but then a week before the election, A had a heart
>> attack. The actual scores, with 3 ballots still to count from A's
>> former stronghold precinct, are:
>>
>> 48: B
>> 49: C
>>
>> I guess C wasn't so dominant in top-ratings after all. Once we
>> count those last three ballots, we'll have a clear winner here,
>> and there's every chance it could be B.
>>
>> The suggestion that "B is better" because of
>> some guess that 3 truncators are "likely" attempting some
>> strategy is absurd.
>>
>>
>> No, B is better because B has majority approval where C is
>> rejected by a majority. The argument about likely truncation is
>> merely how IBIFA went wrong, not how U/P got it right.
>> ...Again, I don't regard this as a knockdown argument against
>> IBIFA. It's only one scenario; a roughly plausible one, but not
>> particularly likely. I think we should probably drop this. But I
>> do think it demonstrates pretty conclusively that IBIFA at least
>> isn't strictly dominant. After all, as long as we're making up
>> arbitrary scenarios, we can arbitrarily assume that the 3 A
>> voters are in fact attempting strategy. Punishing strategy might
>> not be the worst thing in the world, but rather than punishing 48
>> voters for the strategy of 3, it would be better to ignore the 3.
>>
>> I'll write a broader response in a minute.
>>
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