[EM] Strategy-free criterion
Chris Benham
cbenhamau at yahoo.com.au
Sat Jun 22 19:14:44 PDT 2024
CLC,
> An equal-ranking isn’t a way to express indifference..
Of course that is exactly what it is.
> ...(or else equal-ranks would never happen) ..
(For this email I'll refrain from subtle sarcasm.) That doesn't make any
sense.
> Learning that a voter refuses to say whether they prefer Bob or Bill
> provides an important piece of information.
I can't imagine what that might be if it was the case, but we haven't
"learn't" any such thing. The voter hasn't expressed a preference
between Bob and Bill. Sans mind-reading technology I don't see that we
have any choice other than following the Occam's Razor principle and
assume the voter has no preference between Bob and Bill.
> Here's an example of a realistic situation where this applies. Say we
> have a paired matchup where Donald Trump defeats Mitt Romney by
> 36%-29%, because most Republicans prefer Trump. Most Democrats
> truncate their ballots and refuse to rank either, which might hurt
> them: if they support Romney, he might defeat the Democratic candidate.
>
> In this situation, we have to work out what theiropinions are.
I don't see why. And how? And who exactly is this "we"?
> So, isn't it reasonable to say this isn't a real victory for Trump at
> all?
No, it is not reasonable.
> It's perfectly reasonable—probable, even—that Romney is much more
> popular than he looks here, and the only reason Trump looks like he
> beats is because he has a small but extreme base of supporters.
It may or may not be an accurate guess, but I can't see anything
"reasonable" about it.
> Similarly, what if some Alexandria Ocasio-Cortez voters bullet-vote
> for moral reasons or because they're overconfident in their chances of
> victory, and don't want to give a win away to a more moderate
> Democrat? Wouldn't it reasonable to infer that these AOC supporters,
> despite ranking all the viable candidates equally, /do/actually
> support Clinton as their second choice?
Same answer: No.
There is more than one way to define "popular". And the incentives of
the method are obviously a big factor in our guessing about how well the
ballots reflect the voters' sincere preferences.
Chris B.
On 23/06/2024 8:01 am, Closed Limelike Curves wrote:
> Chris, sorry if I wasn't clear enough with this statement:
>
> An equal-ranking isn’t a way to express indifference (or else
> equal-ranks would never happen); it’s a way of pleading the fifth.
> Learng that a voter refuses to say whether they prefer Bob or Bill
> provides an important piece of information.
>
> In the United States, Americans have a constitutional right to refuse
> to answer any question they're asked by a police officer or other
> government official. This is guaranteed by the fifth amendment, and is
> intended to prevent forced confessions. This extends to guilty pleas,
> and someone who invokes this right is described as "pleading the fifth
> (amendment)".
>
> Someone who pleads the fifth, in response to an accusation of the
> crime, is saying "I refuse to provide this information, because it
> might be harmful to me, or because it might violate my privacy ."
>
> Here's an example of a realistic situation where this applies. Say we
> have a paired matchup where Donald Trump defeats Mitt Romney by
> 36%-29%, because most Republicans prefer Trump. Most Democrats
> truncate their ballots and refuse to rank either, which might hurt
> them: if they support Romney, he might defeat the Democratic candidate.
>
> In this situation, we have to work out what theiropinions are. So,
> isn't it reasonable to say this isn't a real victory for Trump at all?
> It's perfectly reasonable—probable, even—that Romney is much more
> popular than he looks here, and the only reason Trump looks like he
> beats is because he has a small but extreme base of supporters.
> Similarly, what if some Alexandria Ocasio-Cortez voters bullet-vote
> for moral reasons or because they're overconfident in their chances of
> victory, and don't want to give a win away to a more moderate
> Democrat? Wouldn't it reasonable to infer that these AOC supporters,
> despite ranking all the viable candidates equally, /do/actually
> support Clinton as their second choice?
>
>
> On Mon, Jun 10, 2024 at 4:35 AM Chris Benham <cbenhamau at yahoo.com.au>
> wrote:
>
> CLC,
>
> I assume no-one posts a ballot "intending to be irrelevant" (and
> whether they do or not I don't see as relevant).
>
> Normally I wouldn't expect irrelevant ballots to be literally
> "empty", just containing no information about any of the remotely
> viable information.
>
>> An equal-ranking isn’t a way to express indifference (or else
>> equal-ranks would never happen); it’s a way of pleading the fifth
>
> What?
>
>> Learning that a voter refuses to say whether they prefer Bob or
>> Bill provides an important piece of information.
>>
> Which is?
>
>> Learning a voter has cast a completely blank ballot is an extreme
>> case, where the ballot provides a very important piece of
>> information: it means the voter expects a participation failure,
>> because a nonempty ballot will hurt them.
>
> But an empty one might "help" them ?? Hilarious.
>
>> A rational response to this is to raise the threshold for a
>> defeat, because setting the bar for a defeat closer to 50%
>> prevents cycles (and therefore participation failures). In other
>> words, these ballots are /very/ relevant.
>
> Of course, you anonymous STAR Voting advocate.
>
> Chris B.
>
> On 7/06/2024 1:33 am, Closed Limelike Curves wrote:
>> Yeah, MAMPO seems like it might behave more sensibly there.
>>
>> IIB doesn’t make sense to me outside of positional voting systems
>> (which trivially satisfy it). If an empty ballot was genuinely
>> intended to be irrelevant, the voter wouldn’t have cast it in the
>> first place. An equal-ranking isn’t a way to express indifference
>> (or else equal-ranks would never happen); it’s a way of pleading
>> the fifth. Learning that a voter refuses to say whether they
>> prefer Bob or Bill provides an important piece of information.
>>
>> Learning a voter has cast a completely blank ballot is an extreme
>> case, where the ballot provides a very important piece of
>> information: it means the voter expects a participation failure,
>> because a nonempty ballot will hurt them.
>>
>> A rational response to this is to raise the threshold for a
>> defeat, because setting the bar for a defeat closer to 50%
>> prevents cycles (and therefore participation failures). In other
>> words, these ballots are /very/ relevant.
>>
>> On Thu, Jun 6, 2024 at 7:40 AM Chris Benham
>> <cbenhamau at yahoo.com.au> wrote:
>>
>> Kevin,
>>
>>> I would not like to see SFC as totally obsolete, since it was one of the motivating
>>> criteria (along with MD and weak FBC) for my methods MDDA and MAMPO :)
>>
>> Inventing those methods was some achievement as a thought
>> experiment to demonstrate that certain criteria are mutually
>> compatible.
>>
>> But MDDA spectacularly fails the maximum-absurdity criterion
>> Mono-add-Plump, a very interesting fact that isn't mentioned
>> on its electowiki page.
>>
>> https://electowiki.org/wiki/Majority_Defeat_Disqualification_Approval
>>>
>>>
>>> Procedure
>>>
>>> The voter submits a ranking of the candidates. The
>>> candidates explicitly ranked are considered/approved/by that
>>> voter.
>>>
>>> A candidate is/dominated/if more than half of the voters
>>> rank some other candidate strictly above him.
>>>
>>> All dominated candidates are eliminated, unless this would
>>> eliminate all the candidates.
>>>
>>> Of remaining candidates, the one approved by the most voters
>>> is elected.
>>>
>>>
>>> Criteria
>>>
>>> *MDDA*satisfies theFavorite Betrayal criterion
>>> <https://electowiki.org/wiki/Favorite_Betrayal_criterion>,Strategy-Free
>>> criterion
>>> <https://electowiki.org/wiki/Strategy-Free_criterion>,
>>> theStrong Defensive Strategy criterion
>>> <https://electowiki.org/wiki/Strong_Defensive_Strategy_criterion>(andMinimal
>>> Defense criterion
>>> <https://electowiki.org/wiki/Minimal_Defense_criterion>),
>>> andmonotonicity
>>> <https://electowiki.org/wiki/Monotonicity_criterion>.
>>>
>>> It failsClone-Winner
>>> <https://electowiki.org/wiki/Strategic_nomination>,
>>> thePlurality criterion
>>> <https://electowiki.org/wiki/Plurality_criterion>,
>>> theGeneralized Strategy-Free criterion
>>> <https://electowiki.org/wiki/Generalized_Strategy-Free_criterion>,
>>> theCondorcet criterion
>>> <https://electowiki.org/wiki/Condorcet_criterion>, theSmith
>>> criterion
>>> <https://electowiki.org/wiki/Smith_set>,Participation
>>> <https://electowiki.org/wiki/Participation_criterion>,
>>> theMajority criterion for solid coalitions
>>> <https://electowiki.org/wiki/Majority_criterion>,
>>> andLater-no-harm
>>> <https://electowiki.org/wiki/Later-no-harm_criterion>.
>>>
>>>
>>
>> 25: A>B
>> 26: B>C
>> 23: C>A
>> 04: C
>>
>> 78 ballots (majority threshold = 40)
>>
>> B>C 51-27, C>A 53-25, A>B 48-26. Implicit Approval scores: C 53, B 51, A 48.
>>
>> All the candidates have a majority-strength defeat, so none are eliminated and the most approved candidate, C, wins.
>>
>> Say we now add 22 ballots that all plump (i.e. bullet vote) for C:
>>
>> 25: A>B
>> 26: B>C
>> 23: C>A
>> 26: C
>>
>> 100 ballots (majority threshold = 51)
>>
>> B>C 51-49, C>A 75-25, A>B 48-26. Implicit Approval scores: C 75, B 51, A 48.
>>
>> Now only B is without a "majority-strength defeat", so the winner changes from C to B.
>>
>> Of course the method also fails Irrelevant Ballots Independence. If we now add 3 ballots that plump for X, the majority threshold rises to 52 and so C's majority-strength defeat goes away and C wins again by being the most approved candidate.
>>
>> This demonstration of Mono-add-Plump failure doesn't apply to MAMPO, but that method would also fail Irrelevant Ballots Independence. It may be far less bad.
>>
>> https://electowiki.org/wiki/Majority_Approval,_Minimum_Pairwise_Opposition
>>
>>>
>>> Procedure
>>>
>>> The voter submits a ranking of the candidates. The
>>> candidates explicitly ranked are considered/approved/by that
>>> voter.
>>>
>>> The/score/for candidate/X/against candidate/Y/is equal to
>>> the number of voters ranking/X/above/Y/. The/max score/of
>>> candidate/X/is the largest score of any other candidate
>>> against/X/.
>>>
>>> If nobody is approved by more than half of the voters, then
>>> the candidate approved by the most voters is elected.
>>>
>>> Otherwise, the candidate with the lowest max score, who is
>>> approved by more than half of the voters, is elected.
>>>
>>
>> Chris B.
>>
>>
>>
>> On 2/06/2024 7:23 am, Kevin Venzke wrote:
>>> Hi all,
>>>
>>> When I test for SFC compliance the rule on cast votes is that if there is no
>>> majority over A, and A has a majority over B, then B can't win.
>>>
>>> This is kind of a flip side of MD / SDSC because, if you were forced to explain MD
>>> in terms of a graph of majority-strength defeats, it would say that if A has a
>>> majority over B and B doesn't have a majority over anyone, then B can't win.
>>>
>>> MD basically says that if there are two frontrunners and everyone truncates their
>>> less liked frontrunner, then the worse frontrunner won't win. If this property
>>> doesn't hold, it means the majority has done something to stop the method from
>>> "seeing" their majority, which is surely that they ranked other candidates above
>>> the preferred frontrunner. So MD is mostly about compromise incentive.
>>>
>>> SFC is probably going to be about truncation. When a method fails it, most likely
>>> it's because the majority gave the election away to a less liked compromise choice.
>>> For example:
>>>
>>> 20 C>A>B
>>> 35 A>B
>>> 5 B
>>> 40 D
>>>
>>> Here B is the implicit approval winner, but by SFC B should not win, because it
>>> means it was not safe for the A voters to rank B.
>>>
>>> I would not like to see SFC as totally obsolete, since it was one of the motivating
>>> criteria (along with MD and weak FBC) for my methods MDDA and MAMPO :)
>>>
>>> Kevin
>>> votingmethods.net <http://votingmethods.net>
>>
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