[EM] Shortlisting

[Kristofer Munsterhjelm]

On 2026-01-30 18:24, Joseph Malkevitch via Election-Methods wrote:
> Dear Colleagues,
> 
> The linked paper offers some interesting ideas related to elections, 
> voting and social choice:
> 
> https://arxiv.org/pdf/2601.21277 <https://arxiv.org/pdf/2601.21277>

That shortlisting is different from PR is a good point. It reminds me of 
a similar thought I've been having about runoffs vs single-winner 
(single-round) methods.

A single-winner method should find the best winner according to the 
information provided by the ballots; or at least find a winner that can 
be defended by some criteria and doesn't violate others, since "best" 
may be difficult to discern due to incommensurability, etc.

But a runoff method is somewhat different. It should, I think, find a 
set of candidates who could plausbly be the winner if the people were to 
investigate that set more closely.

In a way, it is a shortlisting operation, but instead of using a 
distinct group (the shortlisters), it instead uses noisy ballot data to 
determine a set of candidates each of whom, were the noise of a 
particular type, could plausibly be the winner.

The candidates continuing to the general/second round probably should 
include the winner of a good single-winner ballot applied to the primary 
ballots, because one model of noise is "no noise" or "whatever noise the 
single-winner method can most easily handle". This immediately makes it 
clear that if the single-winner method is Condorcet, then the general 
election candidate set can't just be a multiwinner PR solution, since 
Droop proportionality is incompatible with Condorcet.

OTOH, just picking the n highest ranked candidates according to the 
single-winner method has its flaws, too: something like block ranked 
pairs is really clone-dependent (just clone the RP winner n times to 
fill the general).

So presumably, the solution of finding a good candidate set for a runoff 
is distinct from both "just use PR" and "just use bloc results". But 
what is it?

(Also, such a runoff concept would critically depend on the voters being 
given more information about the candidates who win the primary so they 
can refine their opinions before the general. Thus it isn't useful for 
"instant" runoff methods, because there's no such period of deliberation.)

-km