[EM] Strategy-free criterion

[Closed Limelike Curves]

I think Minimal Defense can be justified as strongly desirable without any
reference to strategy at all: it's just the majority loser criterion with
truncation. In other words, if a majority of voters refuse to rank a
candidate at all, that candidate cannot win (unless all candidates are
rejected by a majority).

On Fri, May 31, 2024 at 7:57 PM Michael Ossipoff <email9648742 at gmail.com>
wrote:

>
>
> On Fri, May 31, 2024 at 19:04 Chris Benham <cbenhamau at yahoo.com.au> wrote:
>
>> It [SDC] doesn't talk about just any "Condorcet winner".  It says that if
>> A is the sincere CW and more than half the voters vote A above B, then the
>> voters who prefer B to A can't make B win just by truncating.
>>
>
> Exactly. That was what I meant to say. Forgive me if I didn’t say it.
>
> But maybe they can if less than half the voters vote A over B (with A
>> still being the sincere CW and pairwise-beating B) and maybe they can by
>> order-reversal Burial.
>>
>
> Of course.
>
> Sincere Defense  [Minimal Defense (MDC)] says that if more than half the
>> voters prefer A to B, they can stop B from winning by voting A over B and
>> truncating against B.  From a Kevin Venzke webpage:
>>
>> https://votingmethods.net/em2005
>>
>> *Minimal Defense*. *(Due to Steve Eppley.)*
>>
>> *If more than half of the voters rank candidate A above candidate B, and
>> don't rank candidate B above anyone, then candidate B must be elected with
>> 0% probability.*
>>
>> Yes.
>
> Steve Eppley has defined and discussed Minimal Defense here [broken link]
>> <http://alumnus.caltech.edu/~seppley/> and here [broken link]
>> <http://alumnus.caltech.edu/~seppley/Strategic%20Indifference.htm>.
>> Satisfaction of this criterion implies compliance with Mike Ossipoff's *strong
>> defensive strategy criterion*, although the reverse is not necessarily
>> true. That criterion can be found here [broken link]
>> <http://www.barnsdle.demon.co.uk/vote/stfree.html>.
>>
>> Yes, it’s true that they aren’t the same, because MDC requires
> stipulation of a balloting (usually ranked)…but SDSC is universally
> applicable, because it’s a preference-&-sincere
> criterion.
>
> Note that the ballot must accept all preference orders; in particular, the
>> voter must be able to rank multiple candidates above no one (usually by
>> truncation), and to *strictly* rank any number of candidates. If the
>> word "strictly" were dropped, then Approval
>> <https://votingmethods.net/em2005#methappr> would satisfy, as could
>> other methods using a "limited slot" ballot
>>
>> Yes, Approval doesn’t pass SDSC, due to the definition of “sincere” for
> the preference-sincere criteria, though SDSC applies to Approval.  …& I
> didn’t apply MDC to Approval.
>
> Because I prefer preference-sincere criteria, I didn’t define a version of
> MDC for Approval-balloting.
>
> Anyway, MDC was Eppley’s version. …& the version that was
> generally-accepted. …& therefore the one that I usually refer to.  …which
> is fine, because we only use it for comparison of rank-methods.
>
>> . (Approval <https://votingmethods.net/em2005#methappr> satisfies Mike
>> Ossipoff's *weak defensive strategy criterion* for this reason.) In my
>> opinion, the word "strictly" should be dropped, since Approval
>> <https://votingmethods.net/em2005#methappr> can already be made to
>> satisfy Minimal Defense just by allowing the voter to number his approved
>> candidates, without analyzing the ballot any differently.
>>
>> Sure, if that would make the votes-only criteria apply to Approval, Score
> & STAR.
>
>> Minimal Defense deals with the issue of what a majority need to do to get
>> their opinion counted. Specifically, if they are united in preferring
>> candidate A to candidate B, all they have to do is not rank B. They need
>> not do anything special regarding A. For instance, on these ballots:
>>
>> 49 B
>> 13 C>A
>> 13 D>A
>> 13 E>A
>> 12 F>A
>>
>> The A>B voters (i.e., the voters preferring A to B) are a majority, and
>> do not rank B at all, so that Minimal Defense guarantees that B won't win.
>> However, candidate B is the winner in e.g. Plurality
>> <https://votingmethods.net/em2005#methfpp>, Instant Runoff
>> <https://votingmethods.net/em2005#methirv>, and Descending Solid
>> Coalitions <https://votingmethods.net/em2005#methdsc>. Under these
>> methods, if the A>B majority want to prevent B from being elected, they
>> need to insincerely raise candidate A in their rankings.
>>
>> —& that problem remains to some significant degree with any Condorcet
> version that isn’t autodeterent.
>
>> A more general way to view this problem is by noting that this election
>> is primarily a contest between A and B. In that light, it would be very
>> undesirable for the election method to elect the *wrong one* of these
>> two. Minimal Defense ensures that the method can't be "confused" by the
>> introduction of weaker candidates preferred to the major candidates.
>>
>> As for the methods which satisfy Minimal Defense, Schulze
>> <https://votingmethods.net/em2005#methsch> elects A in the above
>> scenario (as would any Condorcet method
>> <https://votingmethods.net/em2005#methcond>), and Equal Majorities
>> <https://votingmethods.net/em2005#methcdtt> elects either C, D, E, or F.
>> (This is because all candidates besides B are in the CDTT; when Random
>> Ballot <https://votingmethods.net/em2005#methrb> is used to break the
>> tie, only these four candidates have any first preferences. Minimum
>> Opposition <https://votingmethods.net/em2005#methmmpo> gives the same
>> result, incidentally, although it doesn't satisfy Minimal Defense when
>> there are more than three candidates.)
>>
>>
>>
>> On 1/06/2024 8:38 am, Closed Limelike Curves wrote:
>>
>> OK, so SFC prevents offensive truncation from defeating the Condorcet
>> winner, while minimal defense provides a simple way to stop order-reversal?
>>
>>
>> On Fri, May 31, 2024 at 4:01 PM Michael Ossipoff <email9648742 at gmail.com>
>> wrote:
>>
>>> Evidently, then,  SFC merely says that the candidate can’t win without
>>> order-reversal, while Minimal-Defense says he can’t win at all if the
>>> minimal defensive-strategy is used.
>>>
>>> It seems to me that Eppley’s Minimal-Defense was the votes-only
>>> criterion based on SDSC.
>>>
>>> …& that SDSC was the original, preference-&-sincerity version.
>>>
>>> I preferred preference-&-sincerity because of its universal
>>> applicability, where votes-only had to stipulate a balloting.
>>>
>>> On Fri, May 31, 2024 at 12:33 Chris Benham <cbenhamau at yahoo.com.au>
>>> wrote:
>>>
>>>> Why are we having a public discussion about a voting method criterion
>>>> without anyone giving its definition, and with apparently most of the
>>>> participants in the discussion knowing nothing about it besides its name?
>>>>
>>>> https://electowiki.org/wiki/Strategy-free_criterion
>>>>
>>>> The *strategy-free criterion* is a voting system criterion
>>>> <https://electowiki.org/wiki/Voting_system_criterion> for evaluating voting
>>>> systems <https://electowiki.org/wiki/Voting_system>.
>>>> Definitions
>>>>
>>>> A sincere vote is one with no falsified preferences or preferences left
>>>> unspecified when the election method allows them to be specified (in
>>>> addition to the preferences already specified).
>>>>
>>>> One candidate is preferred over another candidate if, in a one-on-one
>>>> competition, more voters prefer the first candidate than prefer the other
>>>> candidate.
>>>>
>>>> If one candidate is preferred over each of the other candidates, that
>>>> candidate is called "Condorcet candidate" or "Condorcet winner".
>>>> Statement of criterion
>>>>
>>>> If a Condorcet candidate exists, and if a majority prefers this
>>>> candidate to another candidate, then the other candidate should not win if
>>>> that majority votes sincerely and no other voter falsifies any preferences.
>>>>
>>>> In a ranked method, it is nearly equivalent to say:
>>>>
>>>> If more than half of the voters rank *x* above *y*, and there is no
>>>> candidate *z* whom more than half of the voters rank above *x*, then
>>>> *y* must not be elected.
>>>>
>>>>
>>>> I think this evolved into the Minimal Defense criterion, the
>>>> "votes-only version" of which says that if more than half the voters vote A
>>>> over B and B no higher than equal-bottom then B can't win.
>>>>
>>>
>>>>
>>>>
>>>>
>>>> On 31/05/2024 9:46 pm, Michael Ossipoff wrote:
>>>>
>>>> Some time ago, I wrote a criterion that I called
>>>> Strategy-Free-Criterion (SFC).
>>>>
>>>> Is that what you were referring to?
>>>>
>>>> It was about a circumstance in which wv Condorcet is strategy-free. At
>>>> that time, autodeterence hadn’t been considered.
>>>>
>>>> SFC didn’t catch-on, & I haven’t heard mention of it lately, & so I
>>>> don’t know it’s definition. But wv Condorcet is strategy-free in a
>>>> meaningful sense.
>>>>
>>>> On Fri, May 31, 2024 at 05:07 Michael Ossipoff <email9648742 at gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Wed, May 29, 2024 at 14:15 Closed Limelike Curves <
>>>>> closed.limelike.curves at gmail.com>
>>>>> Ppwrote:
>>>>>
>>>>>> I'm trying to work out how the strategy-free criterion actually
>>>>>> relates to strategy, because it just sounds like it means the
>>>>>> majority-Condorcet criterion ("if a candidate majority-beats every other,
>>>>>> they have to win if everyone is honest"). @Michael Ossipoff ?
>>>>>>
>>>>>  Closed, isn’t “Strategy-Free Criterion” your new name for FBC.
>>>>>
>>>>> It’s a very inaccurate name. FBC-complying methods aren’t
>>>>> strategy-free in any sense.
>>>>>
>>>>>  But they’re free of any need for *drastic* defensive strategy
>>>>> (favorite-burial or any defensive order-reversal).
>>>>>
>>>>> You want strategy-free? The wv Condorcet methods, such as RP(wv) &
>>>>> MinMax(wv), are strategy-free in a meaningful sense…effectively free of
>>>>> need for any defensive strategy…due to their autodeterence.
>>>>>
>>>>
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>>>>
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>>>
>>
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