[EM] Improvement to Ranked Robin method

Thu Mar 31 10:10:24 PDT 2022

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
>> ----
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>> info
>