[EM] Improvement to Ranked Robin method
Forest Simmons
forest.simmons21 at gmail.com
Tue Apr 5 21:03:22 PDT 2022
El sáb., 2 de abr. de 2022 9:41 p. m., Richard, the VoteFair guy <
electionmethods at votefair.org> escribió:
> On 4/1/2022 6:24 PM, Forest Simmons wrote:
> > ...
> > Here are two versions of decloned Copeland that are not prone to ties:
> >
> > 1.Elect the candidate that, on the greatest number of ballots,
> > pairwise defeats the candidate designated "worst."
> > ...
> > 2. Elect the candidate that, on the fewest number of ballots, is
> > pairwise defeated by the candidate designated "best."
>
> Both of these ways of resolving Copeland ties are more difficult to
> understand -- for most voters -- than the current version.
>
These are not ways of resolving Copeland ties ... rather they are two
succinctly stated complete versions of Copeland that only vanishingly
rarely require any tie breaker at all, let alone one as elaborate as you
are suggesting.
>
> As a further barrier to understanding, these definitions involve
> recursion.
Recursion? Who said recursion? Where did you get that impression? Where is
the recursion in ...
... elect the candidate that, on the fewest number of ballots, is pairwise
defeated by the ballot favorite ....
To spell it out in complete detail ... just open each ballot B and, after
identifying the first preference X on each ballot B, give a demerit to each
candidate Y defeated pairwise by candidate X.
After tallying all of the ballots in this same fashion, elect the candidate
with the fewest demerits.
[That's all there is ... don't try reading something complicated into it
;-)
If another method seems simpler, it's only because you are more familiar
with it.]
A Condorcet candidate will have no demerits because, by definition a
Condorcet candidate is not defeated pairwise.
The key to clone independence is focusing on defeats incurred by the ballot
favorites, rather than giving all pairwise defeats equal weight.
That's even more difficult to procedurally understand than a pairwise
> matrix.
> The goal of the Ranked Robin method (according to the description on
> Electowiki) is to provide a method that is reasonably easy to
> understand, yet uses ranked choice ballots and yields reasonably fair
> results.
>
> As I said, I'm proposing that the method be made even easier to
> understand by using pairwise support counts, which are directly
> countable from the ballots, without involving a pairwise matrix.
>
> Regarding your desire to protect against clone failures, those are just
> one special kind of "irrelevant alternative," as in IIA (independence of
> irrelevant alternatives). Personally I'm more concerned about reducing
> all kinds of irrelevant alternatives. In this case I'm concerned that
> attempts to fully eliminate clone independence failures might have the
> side effect of increasing the rates of other kinds of IIA failures.
>
> Richard Fobes
> The VoteFair guy
>
>
> On 4/1/2022 6:24 PM, Forest Simmons wrote:
> > Besides being prone to ties, Copeland also suffers from Clone
> > Dependence, which makes it inferior to IRV in that regard.
> >
> > Here are two versions of decloned Copeland that are not prone to ties:
> >
> > 1.Elect the candidate that, on the greatest number of ballots, pairwise
> > defeats the candidate designated "worst."
> >
> > That is the burial resistant version of decloned Copeland.
> >
> > The other version, that may be more appealing to some people, is this:
> >
> > 2. Elect the candidate that, on the fewest number of ballots, is
> > pairwise defeated by the candidate designated "best."
> >
> > Both of these methods are monotonic, clone free, and "Round Robin
> > Efficient."
> >
> > It is practically impossible for either method to yield a tied result in
> > an actual political election involving hundreds of ballots.
> >
> > Because of that fact, the obligatory tie breaker does not need the
> > special scrutiny that is so important for ordinary clone dependent
> Copeland.
> >
> > Random Favorite would be the simplest ... and perfectly adequate tie
> > breaker.
> >
> > At the other end of the spectrum, method one could serve as the tie
> > breaker for method two, and vice-versa.
> >
> > Between those possibilities there are many others that are also
> > perfectly adequate.
> >
> > -Forest
> >
> >
> >
> >
> > El jue., 31 de mar. de 2022 12:04 p. m., Colin Champion
> > <colin.champion at routemaster.app <mailto:colin.champion at routemaster.app>>
> > escribió:
> >
> > Richard – there are two ways of using a Borda tiebreak, sometimes
> > written "Llull//Borda" and "Llull,Borda". It sounds like you
> > understood me to be attributing "Llull,Borda" to you while you were
> > actually advocating "Llull//Borda". (I have no idea which of these
> > was Dasgupta and Maskin’s preference – I don’t think they were
> > clear.) Certainly Llull//Borda reduces to a plurality choice between
> > two tied candidates.
> > Other tiebreaks (eg. minimax) can be used in the same two ways,
> > which is why a fairly general notation exists. I can't say I like it
> > as a notation, since it's far from self-explanatory.
> > Colin
> >
> > On 31/03/2022 18:10, Richard, the VoteFair guy wrote:
> >> On 3/30/2022 11:51 PM, Colin Champion wrote:
> >> > ... is the candidate with the highest support count not the
> >> > candidate with the highest Borda score? Have you not reinvented
> >> > Dasgupta-Maskin?
> >>
> >> Borda count is a positional voting method:
> >>
> >> https://en.wikipedia.org/wiki/Positional_voting
> >>
> >> As a tie breaker, only the candidates who are tied are considered
> >> in this count.
> >>
> >> When the tie is between just two candidates, the Borda count would
> >> still use the (positional) numbers assigned by the voters.
> >>
> >> In contrast, I'm recommending a counting method that disregards
> >> which position contains the mark being counted. So a
> >> two-candidate tie becomes simple plurality counting.
> >>
> >> To repeat, I'm suggesting breaking a tie by using pairwise support
> >> counts. On one ballot the pairwise support count is the number of
> >> candidates who are ranked lower than the candidate getting the
> >> support count. Those counts are added across all the ballots to
> >> yield that candidate's pairwise support count.
> >>
> >> A big advantage is that it can be counted directly from the
> >> ballots, without first creating a pairwise matrix. Although
> >> software would use the pairwise matrix approach, voters and the
> >> legal description and the tabulated results would not mention the
> >> pairwise matrix.
> >>
> >> Richard Fobes
> >> The VoteFair guy
> >>
> >>
> >> On 3/30/2022 11:51 PM, Colin Champion wrote:
> >>> Richard – is the candidate with the highest support count not the
> >>> candidate with the highest Borda score? Have you not reinvented
> >>> Dasgupta-Maskin?
> >>> Colin
> >>>
> >>>
> >>> On 31/03/2022 05:58, Richard, the VoteFair guy wrote:
> >>>> Here I'm suggesting a way to improve the recently (fall 2021)
> >>>> created
> >>>> "Ranked Robin" method, which is described at Electowiki at this
> >>>> link:
> >>>>
> >>>> https://electowiki.org/wiki/Ranked_Robin
> >>>>
> >>>> The improvement is to replace the first-level tie breaker -- which
> >>>> looks at margins calculated from the pairwise matrix -- with
> >>>> "pairwise
> >>>> support counts" -- which are easily described without using any
> >>>> numbers from the pairwise matrix.
> >>>>
> >>>> Starting from the beginning ...
> >>>>
> >>>> Currently the Ranked Robin method is described this way:
> >>>>
> >>>> "Elect the candidate who pairwise beats the greatest number of
> >>>> candidates."
> >>>>
> >>>> That's the method described by Ramon Llull (in 1299).
> >>>>
> >>>> According to Electowiki that's been improved to become the
> Copeland
> >>>> method, which elects "the candidate with the most (pairwise
> >>>> victories
> >>>> minus pairwise defeats)."
> >>>>
> >>>> According to Wikipedia the Copeland method doesn't do the
> >>>> subtraction
> >>>> and instead adds "half the number of candidates with whom he or
> she
> >>>> has a preference tie."
> >>>>
> >>>> All of these Copeland method variations produce lots of ties.
> >>>>
> >>>> So of course the Ranked Robin method needs tie breakers. Here's
> >>>> the
> >>>> first-level tie breaker as it's currently specified:
> >>>>
> >>>> "For each finalist, subtract the number of votes preferring each
> >>>> other
> >>>> finalist from the number of votes preferring them over each other
> >>>> finalist. The finalist with the greatest total difference is
> >>>> elected."
> >>>>
> >>>> A big disadvantage of this Ranked Robin tie breaker is that it
> uses
> >>>> numbers from the pairwise matrix. Yet one of the stated goals
> >>>> of the
> >>>> Ranked Robin method is to avoid confusing voters with the pairwise
> >>>> matrix.
> >>>>
> >>>> Therefore I suggest replacing this tie-breaker method with the
> >>>> use of
> >>>> "pairwise support counts." These counts are part of the "Instant
> >>>> Pairwise Elimination" (IPE) method, which is described at
> >>>> Electowiki
> >>>> at this link:
> >>>>
> >>>> https://electowiki.org/wiki/Instant_Pairwise_Elimination
> >>>>
> >>>> It says:
> >>>>
> >>>> "If an elimination round has no pairwise-losing candidate, then
> the
> >>>> method eliminates the candidate with the largest pairwise
> >>>> opposition
> >>>> count, which is determined by counting on each ballot the number
> of
> >>>> not-yet-eliminated candidates who are ranked above that
> >>>> candidate, and
> >>>> adding those numbers across all the ballots. If there is a tie
> >>>> for the
> >>>> largest pairwise opposition count, the method eliminates the
> >>>> candidate
> >>>> with the smallest pairwise support count, which similarly counts
> >>>> support rather than opposition. ..."
> >>>>
> >>>> Of course the second-level tie-breaker would be to use pairwise
> >>>> opposition counts. (The pairwise support counts and pairwise
> >>>> opposition counts are not always symmetrical.)
> >>>>
> >>>> Notice that the numbers in the pairwise matrix do not need to be
> >>>> mentioned.
> >>>>
> >>>> Yes, the software will calculate the pairwise support counts
> >>>> from the
> >>>> numbers in the pairwise matrix. But that fact doesn't need to be
> >>>> mentioned -- to the voters, or in the legal description.
> >>>>
> >>>> The resulting improved Ranked Robin method can be described as
> >>>> follows:
> >>>>
> >>>> "The [improved] Ranked Robin method elects the candidate who has
> >>>> the
> >>>> most number of one-on-one wins against every other candidate
> >>>> plus half
> >>>> the number of one-on-one ties. [*] If more than one candidate
> >>>> has the
> >>>> same largest number, the method elects from those tied
> >>>> candidates the
> >>>> candidate with the highest pairwise support count. The pairwise
> >>>> support count for each of the tied candidates is the sum, across
> >>>> all
> >>>> the ballots, of the number of tied [**] candidates who are ranked
> >>>> lower than the candidate whose pairwise support count is being
> >>>> counted."
> >>>>
> >>>> [*] The wording can be adjusted depending on which Copeland
> >>>> variation
> >>>> is desired. Adding the words "minus the number of one-on-one
> >>>> losses"
> >>>> would specify the other variation.
> >>>>
> >>>> [**] Importantly, the ballot marks for the non-tied candidates
> >>>> must be
> >>>> ignored when resolving the tie.
> >>>>
> >>>> When the election results are displayed, they might look something
> >>>> like this, where the names are from the Ranked Robin article,
> >>>> and the
> >>>> numbers don't apply to any particular case:
> >>>>
> >>>>
> >>>> Matchup win and loss counts:
> >>>>
> >>>> Ava: 4 wins (against ...) and 2 losses (to ...)
> >>>>
> >>>> Bianca: 4 wins (against ...) and 2 losses (to ...)
> >>>>
> >>>> Cedric: 3 wins (against ...) and 3 losses (to ...)
> >>>>
> >>>> Deegan: 3 wins (against ...) and 3 losses (to ...)
> >>>>
> >>>> Eli: 2 wins (against ...) and 4 losses (to ...)
> >>>>
> >>>> Fabio: 0 wins and 6 losses
> >>>>
> >>>>
> >>>> The result is a tie between Ava and Bianca because they each
> >>>> have
> >>>> 4 wins, and that's more than any other candidate. Considering
> just
> >>>> these tied candidates, their pairwise support counts are:
> >>>>
> >>>> Ava: 213
> >>>>
> >>>> Bianca: 123
> >>>>
> >>>> So Ava wins!
> >>>>
> >>>>
> >>>> Notice there's no need to show a pairwise matrix!
> >>>>
> >>>> To prevent a potential source of confusion, the Wikipedia article
> >>>> about the Borda count begins with the words "The Borda count is a
> >>>> family of positional voting rules which gives each candidate,
> >>>> for each
> >>>> ballot, a number of points corresponding to the number of
> >>>> candidates
> >>>> ranked lower." The last portion of this sentence describes
> >>>> pairwise
> >>>> support counts, but it has nothing to do with the Borda count.
> The
> >>>> Wikipedia article for "positional voting" correctly says:
> >>>> "Positional
> >>>> voting is a ranked voting electoral system in which the options or
> >>>> candidates receive points based on their rank position on each
> >>>> ballot
> >>>> and the one with the most points overall wins." The remainder of
> >>>> Wikipedia's Borda count article correctly specifies positional
> >>>> voting
> >>>> in the descriptions and examples. The Borda count article at
> >>>> Electowiki does not include this first-sentence mistake. I'm
> >>>> going to
> >>>> let someone else figure out how the first sentence in Wikipedia
> >>>> should
> >>>> be worded. (I'd rather fight other battles.)
> >>>>
> >>>> I'm calling attention to this difference between pairwise support
> >>>> counts and the Borda count because this issue has previously
> caused
> >>>> confusion in this forum.
> >>>>
> >>>> Getting back to the Ranked Robin method, this improved version
> >>>> is not
> >>>> likely to significantly increase the failure rates of the most
> >>>> important failure criteria, and it's likely to reduce some
> >>>> failure rates.
> >>>>
> >>>> Currently the Ranked Robin article claims that the method passes
> >>>> some
> >>>> fairness criteria that it actually doesn't pass. When the Ranked
> >>>> Robin article is improved to include a concise description of the
> >>>> method (which should be near the beginning), some experts here can
> >>>> identify which of the listed "pass" criteria need to be moved to
> >>>> the
> >>>> listed "fail" criteria.
> >>>>
> >>>> Interestingly, the Ranked Robin method and its name were created
> by
> >>>> people who have previously promoted only STAR voting. I'm pleased
> >>>> that they are finally recognizing that STAR ballots are not
> >>>> going to
> >>>> replace ranked choice ballots throughout the US. And that they
> >>>> recognize the need to promote a method that takes advantage of the
> >>>> Forward Party's recommendation of "ranked choice voting."
> >>>>
> >>>> Looking at the broader perspective ...
> >>>>
> >>>> The current version of Ranked Robin already has these advantages:
> >>>>
> >>>> * Uses pairwise vote counting, which looks deeper into the ballot
> >>>> preferences compared to instant-runoff voting.
> >>>>
> >>>> * Is precinct summable.
> >>>>
> >>>> * Allows voters to mark more than one candidate at the same
> ranking
> >>>> level.
> >>>>
> >>>> I suggest making it even easier to understand by using pairwise
> >>>> support counts. This improvement will eliminate the need to
> >>>> educate
> >>>> voters about the pairwise matrix. And I believe this change will
> >>>> still provide a similar level of fairness.
> >>>>
> >>>> Certainly, in multiple ways, it's much better than
> >>>> instant-runoff voting.
> >>>>
> >>>> Richard Fobes
> >>>> The VoteFair guy
> >>>> ----
> >>>> Election-Methods mailing list - see https://electorama.com/em
> >>>> for list
> >>>> info
> >>>
> >
> > ----
> > Election-Methods mailing list - see https://electorama.com/em for
> > list info
> >
> >
> >
> > ----
> > Election-Methods mailing list - see https://electorama.com/em for list
> info
> >
> ----
> Election-Methods mailing list - see https://electorama.com/em for list
> info
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20220405/1c518be4/attachment-0001.html>
More information about the Election-Methods
mailing list