[EM] Best Deterministic Ranked Preference Method?

Kristofer Munsterhjelm km_elmet at t-online.de
Thu Dec 24 15:16:27 PST 2020

On 24/12/2020 22.19, Kevin Venzke wrote:

> Regarding HBH and Weinstein, I'm having a lot of trouble getting this
> to work reasonably. For one thing, I can't find a way to interpret
> single-round Weinstein DSV Approval so that it is monotone. Also, if
> approval can extend into the bottom rank, it violates Plurality a
> lot. I can disallow that, but this creates a lot more monotonicity
> issues.

DSV tends to be nonmonotone in general: in a way, IRV is Plurality DSV.
Brams made a simlar point about a ministerial apportionment method: the
greedy approach could make someone wish they'd been asked to pick a
position *later*. He solved the problem with a negotiation mechanic: if
party X wanted to switch a minister seat with party Y and both agreed,
then it would be done. So some kind of either fix to get out of a local
optimum, or lookahead to avoid getting into that optimum to begin with,
seems to be needed.

About fpA-fpC, one way to get an idea of what a four-candidate fpA-fpC
method may be like could be to investigate elections where clone
independence demands that some candidate wins (e.g. you can get to the
election by cloning A, and B wins in the original three-candidate
fpA-fpC election; then A must win in the new election).

One of the problems of extending fpA-fpC is that there's no obvious
cloneproof way to do first preferences (apart from DAC/DSC). Perhaps
such "clone continuations" could give some ideas.

(But fpA-fpC could also be an uncontinuable dead end. I'll have to check
when I get more RAM to run my manipulability simulations on.)

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