[EM] Best IRV Tweak?

Susan Simmons suzerainsimmons at outlook.com
Mon Jul 19 20:41:22 PDT 2021

Run IRV as usual eliminating one-by-one the candidates with least first rank support among the remaining candidates UNTIL only the winner survives OR the one on the chopping block is found to dominate every other remaining candidate by the covering relation.

If I were an IRV supporter with a firm belief that low first rank support was the best single indicator of inferior support, it might be hard to convince me that a runoff loser should be promoted to election winner solely on the basis that she was unbeaten pairwise among the remaining candidates.

But if she Pareto Dominated them or (more generally) pairwise beat not only them but also every candidate beaten by them (i.e. "covered" them), that extreme domination might convince me of her worthiness of the golden buzzer.

This rule ensures that a member of the Smith set will be elected, which implies that it is immune from the IRV fiasco of Burlington 2008.

Pretty simple: before eliminating a candidate first check to make sure it doesn't cover the the other remaining candidates.

FAQ: How to explain that such a strong candidate could be in danger of elimination?

Answer: It's due to the well known "squeeze effect" wherein surrounding candidates with less depth of support end up intercepting many of the first place votes, thus garnering enough superficial support to survive early elimination, at the expense of the surrounded candidate.

So the cover check is insurance against unmerited squeeze-out.

Not convinced? Compare Yee Diagrams before and after the tweak!

Sent from my MetroPCS 4G LTE Android Device
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