[EM] Strategy-free criterion
Chris Benham
cbenhamau at yahoo.com.au
Fri May 31 22:24:11 PDT 2024
Yes, I don't know where my "Sincere Defense" brain-fart came from. I
meant *Minimal Defense*. (I corrected it below).
Chris B.
On 1/06/2024 11:34 am, Chris Benham wrote:
> It 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.
>
> 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.
>
> Minimal Defense 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./
>>
>> Steve Eppley has defined and discussed Minimal Defensehere [broken
>> link] <http://alumnus.caltech.edu/~seppley/>andhere [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 foundhere [broken
>> link] <http://www.barnsdle.demon.co.uk/vote/stfree.html>.
>>
>> 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, thenApproval
>> <https://votingmethods.net/em2005#methappr>would satisfy, as could
>> other methods using a "limited slot" ballot. (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, sinceApproval
>> <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.
>>
>> 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>, andDescending 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.
>>
>> 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 anyCondorcet method
>> <https://votingmethods.net/em2005#methcond>), andEqual Majorities
>> <https://votingmethods.net/em2005#methcdtt>elects either C, D, E, or
>> F. (This is because all candidates besides B are in the CDTT;
>> whenRandom 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 avoting system criterion
>>> <https://electowiki.org/wiki/Voting_system_criterion>for
>>> evaluatingvoting 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.
>>>
>>>
>>> ----
>>> Election-Methods mailing list - seehttps://electorama.com/em for list info
>>
>> ----
>> Election-Methods mailing list - see https://electorama.com/em for
>> list info
>>
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