[EM] STAR Voting Variations

[Susan Simmons]

SPE, not BTR is Ihe correct (and customary) terminology for this kind of elimination, because the agenda (score order) is set before any of the eliminations take place.

BTR, as in IRV-BTR, is a procedure where there is no "agenda" list .. the order (after the first elimination) is determined on the fly after the eliminations have already begun (which is why BTR methods fail monotonicity), not before the start of the run-off.

The recursive definition was never intended for the public, but only for EM list subscribers and lurkers, to show them that a change of one word ... score to CHAMP (or STAR if you prefer that name) ... could radically improve STAR, making it ISDA compliant while retaining the monotonicity of Score. It just happens that the one word change makes the definition recursive ... a concept that any EM List reader (or any other educated person) should not be afraid to learn about before their brain fossilizes ... and what better context for EM list readers than a message on that list?

To be clear, the intended audience for my messages to the EM list is the subscribers and curious lurkers for the list, not the general public. Like other older EM contributors, I'm trying to help interested new-comers get a better understanding of the various election methods (both good and bad) and the useful principles for comparing them, by walking them through some of the most salient comparisons. Like the oldest EM members, I continue to learn ... including from young people with their fresh perspectives and interesting questions.



Sent from my MetroPCS 4G LTE Android Device


-------- Original message --------
From: Daniel Carrera <dcarrera at gmail.com>
Date: 7/12/21 7:49 PM (GMT-08:00)
To: Susan Simmons <suzerainsimmons at outlook.com>
Cc: election-methods at lists.electorama.com
Subject: Re: [EM] STAR Voting Variations



On Mon, Jul 12, 2021 at 8:41 PM Susan Simmons <suzerainsimmons at outlook.com<mailto:suzerainsimmons at outlook.com>> wrote:
... continuing ...

Here's another small tweak to create a similar, but much improved method ... let's call this tweak of STAR, "CHAMP."

STAR elects the pairwise winner between the score winner X and the candidate Y  who is the score winner among the other candidates (besides X).

CHAMP elects the pairwise winner between the score winner X and the candidate Z who is CHAMP winner among the other candidates (besides X).

It took me a while to figure out what you were saying. So... a recursive definition of CHAMP... Btw, what does CHAMP stand for (if anything)? Let me see if I understand. If I wanted to compute the CHAMP winner I would:

1) Sort the candidates by score.
2) Pick the pairwise winner "X" between the bottom two candidates.
3) Pick the pairwise winner between "X" and the next candidate up.
4) Repeat.

So CHAMP Is kind of like BTR-STV but you are sorting by score instead of first-choice votes? CHAMP = BTR-Score ? Or have I completely misunderstood?


It turns out that this description of CHAMP is just a particularly compact [and elegant, in the eyes of software engineers] reformulation of Sequential Pairwise Elimination (SPE) applied to the "agenda" of candidates listed from least to greatest scores.

SPE is a highly respected method that has been used in many kinds of deliberative bodies for centuries, and recommended by "Robert's Rules of Order" for choosing from among more than two options ... two-at-a time from an agenda with the least promising agenda items listed first. In the CHAMP context "least promising" means lowest score.

CHAMP is clone proof, monotonic, and Condorcet compliant ... what simpler method has this much going for it?

A recursive method will be tough for most people. I studied Lisp and it was a bit of a curve ball for me. I think an SPE definition might be easier to follow even if it is mathematically inelegant.

If I was trying to sell this to the STAR team, I would tell them that they can even keep the same name they have.

STAR = Score Then Automatic Runoff

There is nothing in that name that requires only one runoff. You could repurpose the name to mean that you Score candidates and then run N runoffs from the bottom up. Boom! Now you've turned STAR into a clone proof, monotonic, Condorcet method and hopefully created a method that fans of Score and fans of Condorcet can both get behind.

Am I right to think that your method, and any other BTR-* method is also Smith-efficient?

Cheers,
Daniel
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