[EM] RCIPE version 2
VoteFair
electionmethods at votefair.org
Wed Jul 21 08:25:58 PDT 2021
On 7/21/2021 4:41 AM, Kristofer Munsterhjelm wrote:
> I would of course suggest moving the tiebreaker up here to replace the
> current elimination condition :-)
>
> "Eliminate the candidate who has the smallest one-on-one pairwise count
> against any other remaining candidate."
I tried placing a higher priority on this kind of elimination because it
avoids eliminating the Condorcet loser. However it causes odd and
undesirable behavior regarding Clone Independence and IIA failures.
Using IRV as the tie breaker protects against clone independence
failures -- which means it protects against money-based vote splitting
tactics.
> You need the pairwise matrix to determine the Condorcet loser anyway, so
> there's not much of a gain in complexity.
A major goal of this redesign is to make the method easier to
demonstrate using an animated video.
Introducing the idea of a pairwise matrix would not work well in an
animated video. It's much too difficult for most voters to understand.
Instead, this method can be animated by having upward-pointing arrows
emerge from the marks on a ranked-choice ballot.
For each candidate, the number of those arrows equals the number of
marks to the right of the mark for that candidate. This assumes that
unmarked candidates are marked by default at the far-right, lowest
ranking level.
I'm intending to use candidate names that are readily associated with a
single letter, such as:
Jay (J), Kay (K), Cici (C), Gigi (G)
Each arrow will have the pairwise winner's initial at the top of the
arrow and the pairwise loser's initial at the bottom of the arrow.
That will allow:
* Removing arrows that are associated with the candidate who was just
eliminated
* Using the same arrows both for checking for Condorcet losers -- when
the arrows are grouped into subgroups (one group per candidate, one
subgroup per arrow letter pair) -- and checking for the smallest
pairwise support count -- when the arrows are not subgrouped.
I'm learning that what's easy to describe in words is not necessarily
easy to explain using graphics.
With fewer and fewer people reading, and more and more people expecting
to learn from videos (which are now easy to access, unlike a few decades
ago), I'm trying to make that shift in what I create.
As always, thank you Kristofer for your wise feedback!
Richard Fobes
The VoteFair guy
On 7/21/2021 4:41 AM, Kristofer Munsterhjelm wrote:
> On 21.07.2021 03:19, VoteFair wrote:
>> Version 2 of the Ranked Choice Including Pairwise Elimination (RCIPE)
>> voting method is now coded.
>>
>> Here's a link to the scatter plot that shows its Clone Independence and
>> IIA (Independence of Irrelevant Alternatives) success rates compared to
>> other single-winner methods:
>>
>> https://www.rankedchoiceoregon.org/img/clone_iia_success_rates.jpg
>>
>> Based on Kristofer's feedback on the scatter plot, I've moved the IRV
>> (instant-runoff voting) data points to the top to show that IRV has a
>> zero Clone Independence failure rate. (The CI measurements yield a
>> non-zero CI failure rate because IRV does not specify a tie breaker
>> method and there are lots of lower-level ties in these "stress test"
>> measurements.) I've removed the IRV-BTR data because it's so similar to
>> IRV.
>>
>> Here is how RCIPE version 2 is counted:
>>
>> * Eliminate the "pairwise losing candidate" (Condorcet loser) when there
>> is one.
>>
>> * Calculate a "pairwise support count" for each candidate. Each ballot
>> contributes to that count the number of remaining(!) candidates who are
>> ranked lower than the specified candidate.
>
> I would of course suggest moving the tiebreaker up here to replace the
> current elimination condition :-)
>
> "Eliminate the candidate who has the smallest one-on-one pairwise count
> against any other remaining candidate."
>
> You need the pairwise matrix to determine the Condorcet loser anyway, so
> there's not much of a gain in complexity.
>
> -km
>
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