[EM] Double Defeat Hare

[Ted Stern]

Richard, I believe Double defeat Hare is also known as RCIPE.

https://electowiki.org/wiki/Ranked_Choice_Including_Pairwise_Elimination

On Sat, Jun 22, 2024, 07:43 Richard, the VoteFair guy <
electionmethods at votefair.org> wrote:

> On 6/22/2024 1:31 AM, Chris Benham wrote:
>  > I think those of us who are extra hung-up about frustrating Burial
>  > should look more closely at Double Defeat, Hare.  ...
>
> What is Double Defeat Hare?
>
> I didn't try to find it on Electowiki because lately that website has
> not been responding when I click on links to it.
>
> Richard Fobes
> the VoteFair guy
> (and now the only Richard here)
>
>
> On 6/22/2024 1:31 AM, Chris Benham wrote:
> > Kevin,
> >
> > Something I didn't address in my previous email:
> >
> >>> And what is wrong with your "Improved
> >>> Condorcet Approval" method ?  I think it would be good using
> >>> unrestricted ranking ballots with an explicit approval cutoff.
> >> ICA or C//A (implicit) are not bad. They don't satisfy SFC. In my
> >> recent simulations
> >> on frontrunner truncation strategy, C//A is among the best Condorcet
> >> methods. In
> >> random elections I am disturbed that ICA and C//A are worse than WV
> >> methods at
> >> strong FBC (i.e. what I call compromise incentive).
> >>
> >> You've asked me many times about C//A(explicit) and I still think it's
> >> bad. The
> >> entire notion of C//A(implicit) being good at deterring burial is
> >> based on the
> >> fact that if you use burial to prevent there from being a Condorcet
> >> winner, then in
> >> the "cycle resolution" you cannot prefer any candidate to the one you
> >> raised
> >> insincerely.
> >>
> >> In C//A(explicit), burial only backfires if it actually creates a fake
> >> CW. Creating
> >> a fake cycle is never bad for your favorite.
> >
> > In these mass public elections the chance that an individual voter's
> > ballot will be pivotal is negligible. I would think that if the method
> > is making some attempt to minimise the number of "wasted votes", then
> > many voters would want to be able to express their full sincere ranking
> > and also would at least not mind giving their sincere or semi-sincere
> > approval cutoff. For example in a Hare (aka IRV) election (with
> > unrestricted strict ranking from the top) I can't imagine it ever
> > crossing my mind to vote insincerely (and I never have).
> >
> > Also I think the method needs to have some justification on the
> > assumption that the voters are sincere. So if voters complain "Why
> > aren't I allowed to rank among the candidates I don't approve?" and "How
> > do we know that the voted CW is really the CW if we have been forced to
> > truncate our rankings?", we need some answer that isn't just about
> > "deterring burial".  We could say "Well this is more simple, and it's
> > not strictly a Condorcet method but rather an Approval-Condorcet hybrid
> > that is trying to produce a high SU winner" but I expect that a lot of
> > voters would not be fully satisfied with that answer.  (I wouldn't be.)
> >
> > I have become firmer in my support for Double Defeat (explicit) methods
> > and my favourite of these is Margins-Sorted Approval. Those method allow
> > voters to rank however many candidates they wish and also give a
> > approval cutoff, and no candidate that is pairwise-beaten by a more
> > approved candidate is allowed to win. Much of the time this is by itself
> > decisive.
> >
> > I think those of us who are extra hung-up about frustrating Burial
> > should look more closely at Double Defeat, Hare.  I suspect that it has
> > most of the Condorcet efficiency of an actual Condorcet method while
> > retaining most of the Burial resistance of Hare, while possibly tending
> > to give higher SU winners than both.
> >
> > Chris B.
> >
> > On 21/06/2024 9:32 pm, Kevin Venzke wrote:
> >> Hi Chris,
> >>
> >>> On Mono-add-Plump as a weak version of Participation:
> >>>> Yes but almost all proposals fail Participation, so we will be in a
> >>>> lot of trouble
> >>>> if we insist on this kind of thinking.
> >>> What sort of "trouble"?  I don't see how your conclusion follows from
> >>> your premise. Why do "almost all proposals fail Participation"?  It
> >>> isn't because there is anything inherently wrong with "that kind of
> >>> thinking". It is because it just happens that Participation is very
> >>> expensive (in terms of other desirable criterion compliances, such as
> >>> Condorcet).  But in that way Mono-add-Plump is very very cheap (if not
> >>> free), and some of us are currently "in trouble" due to disregarding
> >>> "this kind of thinking".
> >> What I'm saying is that if we pursue criteria in the vein of
> >> Participation (or
> >> monotonicity), we cut down the list of methods we can consider, and we
> >> aren't
> >> necessarily getting anything of value except that fewer people can
> >> call the method
> >> absurd. What I call inherently of value would be things like sincere
> >> Condorcet
> >> efficiency or reduced strategic incentives.
> >>
> >>> Suppose a mini-bus with a driver is contracted to pick up a group of
> >>> people and take then on a trip to one of  X, Y or Z  after polling the
> >>> passengers on their ranking-preferences among these alternative
> >>> destinations. After the bus is nearly full it is mistakenly assumed
> that
> >>> there will be no more passengers and the driver applies some algorithm
> >>> to the rankings of those present and announces that winning alternative
> >>> is X.
> >>> Then it is learned that there are two more passengers to come to fill
> up
> >>> the bus.  They do so and the driver says to them  "I've polled all the
> >>> other passengers and at the moment the winning destination is X. Where
> >>> would you like to go?" and they reply "X is our first preference and Y
> >>> wouldn't be too bad and we are very glad we aren't gong to Z".
> >>> The driver replies "You prefer Y to Z?  In that case the new winning
> >>> alternative is Y".   Now if these two voters (and perhaps others whose
> >>> first preference was X) were enlightened election-method experts, they
> >>> might think "Obviously this fellow's election-method algorithm fails
> >>> Participation (and presumably Later-no-Harm).  Perhaps it meets
> >>> Condorcet, which we know is incompatible with both Participation and
> >>> Later-no-Harm. Perhaps before we showed up there was a top cycle and
> our
> >>> Y>Z preferences turned Y into the Condorcet winner.
> >>> But we know that Condorcet is also incompatible with Later-no-Help so
> us
> >>> revealing our second preferences could have just as likely helped us,
> so
> >>> I suppose we were just unlucky."
> >>> Or if they were not experts but charitably minded they might think "I
> >>> suppose it is possible that this fellow made an honest mistake due to
> >>> him being thick and us confusing him with too much information".
> >>> Now replay this scenario except this time the new passengers just say
> >>> "Great!  We just really want to go to X and we don't know or care about
> >>> any other destination."  And then the driver says "In that case the
> >>> winning alternative changes from X to Y".
> >>> The response could only be that the destination-decider (supposedly
> >>> purely based on the passengers' stated preferences) is insane (or
> >>> malevolent, in any case illegitimate)  and that Y is obviously an
> >>> illegitimate winner.
> >>> Did you notice a very different vibe from the first case, which was a
> >>> failure of Participation and  Mono-add-Top but not Mono-add-Plump?
> >> The difference in vibe is quite similar to your own difference in vibe
> >> when you
> >> compare these situations.
> >>
> >> In one case, some voters are willing to say "I guess there were other
> >> considerations
> >> in play; we were unlucky" but in the other case they won't go there.
> >> And that's
> >> fine, that is their right.
> >>
> >>> In December 2008 on EM I argued that Schulze's Generalised Majority
> >>> Criterion is a mistaken standard because the concept is vulnerable to
> >>> Mono-add-Plump.
> >> But given their compatibility, isn't that a strange thing to say?
> >>
> >>> Your new MDDA 2 method fails the example I gave:
> >>> 25 A>B
> >>> 26 B>C
> >>> 23 C>A
> >>> 04 C
> >>> (78 ballots, majority threshold = 40)
> >>> Implicit approval scores:  C 53,   B 51,  A 48.   No candidate is
> >>> disqualified due to sub-majority approval.
> >>> B>C 51-27,   C>A 53-25,   A>B 48-26.     All candidates have a
> >>> "majority" strength defeat, so it "isn't possible" to disqualify any
> >>> candidate on that basis.  So, according to the rules of MDDA 2, we
> elect
> >>> the most approved candidate, C.
> >>> Now say we add 22 ballots that plump for C to give:
> >>> 25 A>B
> >>> 26 B>C
> >>> 23 C>A
> >>> 26 C
> >>> (100 ballots, majority threshold = 51)
> >>> Implicit approval scores:  C 75,   B 51,  A 48.   Now A has
> sub-majority
> >>> approval and so is disqualified.
> >>> B>C 51-49,   C>A 75-25,   A>B 48-26.    Now C and A have
> >>> majority-strength defeats and B doesn't, so (according to the rules of
> >>> MDDA 2),  A (again) and C are disqualified leaving B as the new winner.
> >>> The contention that C is the right winner when there were just 78
> >>> ballots but when we add 22 ballots that plump (bullet vote) for C the
> >>> right winner is no longer C is .... completely crazy.
> >> The voters' behavior had a side effect of strengthening B. All sorts
> >> of monotonicity
> >> failures take such an appearance.
> >>
> >> And again, there could be differences in severity, e.g. what percent
> >> of voters think
> >> a given phenomenon is absurd. But I don't find that very interesting
> >> because it
> >> doesn't tell us about the merits of the method. It's basically
> >> marketability.
> >>
> >>>> Well, in an environment where the concept of "median voter" is likely
> >>>> to be meaningful,...
> >>> What "environment" is that?  And why is that the environment the one we
> >>> should primarily focus on?
> >> One where voter and candidate preferences can be explained by an
> >> underlying issue
> >> space. In this case if you could project everyone onto a plane or
> >> spectrum it would
> >> be a bit easy to find the median voter and their preferred candidate.
> >>
> >> I think this usually describes public elections, but it probably
> >> wouldn't cover a
> >> vote on what color is the best, or a vote on what cuisine to have
> >> delivered. So I
> >> think we should probably have IIB for those cases.
> >>
> >>> I think that is the sort of thinking that
> >>> leads some people to support Median Ratings methods, which we know are
> >>> garbage because they fail Dominant Candidate and Irrelevant Ballots
> >>> Independence, and the voters have a strong incentive to just submit
> >>> approval ballots (giving the same result as Approval). And it has led
> >>> you to the absurdity of suggesting a method that fails Mono-add-Plump.
> >> Not at all, median rating methods aren't motivated by the notion of a
> >> single median
> >> voter. There are multiple median voters on different posed questions,
> >> and that's
> >> true on a pairwise matrix as well.
> >>
> >>> I think for the purposes of properly analysing single-winner election
> >>> methods and inspiring the invention of  new ones, we can and should do
> >>> without criteria that refer  to irrelevant ballots dependent "majority"
> >>> thresholds or pairwise defeats.  Those have almost no positive point
> >>> aside from marketing.
> >> You're saying that criteria directly specifying "majority" and not
> >> something else
> >> is what lacks positive points aside from marketing? That could be true.
> >>
> >>> My suggestion for something as close as possible to Minimal Defense:
> >>> *If the number of ballots that vote X above bottom and Y no higher than
> >>> equal-bottom is greater than Y's maximum pairwise support, then Y can't
> >>> win.*
> >> I don't hate that. I don't know what you gain from using "max pairwise
> >> support"
> >> instead of "votes in total."
> >>
> >>> I propose Double Defeat (Implicit) as something that can substitute for
> >>> the votes-only versions of Minimal Defense and SFC and also Plurality.
> >>> *Interpreting ranking (or ranking above equal bottom) as approval, no
> >>> candidate that is pairwise-beaten by a more approved candidate is
> >>> allowed to win.*
> >> It's interesting but it doesn't cover SFC. In an SFC failure scenario
> the
> >> disqualified candidate might very well have more approval than the
> >> candidate who
> >> disqualifies them. The concern is that supporters of the latter gave
> >> the election
> >> away.
> >>
> >>> That already inspires a simple method suggestion:  DDI,MMM: *Elect the
> >>> candidate  not disqualified by Double-Defeat (Implicit) that is highest
> >>> ordered by MinMax(Margins).*
> >>> What do you think of that?
> >> I don't like it but it might be fine.
> >>
> >>> And what is wrong with your "Improved
> >>> Condorcet Approval" method ?  I think it would be good using
> >>> unrestricted ranking ballots with an explicit approval cutoff.
> >> ICA or C//A (implicit) are not bad. They don't satisfy SFC. In my
> >> recent simulations
> >> on frontrunner truncation strategy, C//A is among the best Condorcet
> >> methods. In
> >> random elections I am disturbed that ICA and C//A are worse than WV
> >> methods at
> >> strong FBC (i.e. what I call compromise incentive).
> >>
> >> You've asked me many times about C//A(explicit) and I still think it's
> >> bad. The
> >> entire notion of C//A(implicit) being good at deterring burial is
> >> based on the
> >> fact that if you use burial to prevent there from being a Condorcet
> >> winner, then in
> >> the "cycle resolution" you cannot prefer any candidate to the one you
> >> raised
> >> insincerely.
> >>
> >> In C//A(explicit), burial only backfires if it actually creates a fake
> >> CW. Creating
> >> a fake cycle is never bad for your favorite.
> >>
> >> Kevin
> >> votingmethods.net
> >>
> > ----
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> info
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> info
>
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