[EM] Strategy-free criterion
Chris Benham
cbenhamau at yahoo.com.au
Fri May 31 19:04:02 PDT 2024
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.
Sincere 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.
>>
>>
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>
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