[EM] Election-Methods Digest, Vol 53, Issue 44

[Greg Dennis]

Thanks for the comments, Kevin. I'll try to offer some clarifications
below . . .


> From: Kevin Venzke <stepjak at yahoo.fr>
>
> I want to comment on the first point/reason. I'll quote from the page.
>
>>First and foremost, IRV eliminates the most common type of Condorcet
>>failure --- the "spoiler" scenario --- where the presence of a candidate
>>with little core support causes a Condorcet winner with strong core
>>support to lose.
>
> I don't understand what kind of scenario you're referring to. I thought I
> did, and was going to say that good Condorcet methods don't behave in
> that way. But then I noticed the term "core support," which puzzles me
> in the context of Condorcet spoilers.

My poor wording lead you astray here. When I referred to "the most
common type of Condorcet failure," I did now mean the common common
way in which a Condorcet method fails. I meant the most common
violation of the Condorcet criterion that we see in elections today. I
am not saying anything about Condorcet methods in this paragraph. Both
IRV and Condorcet fix this spoiler problem. I'll improve the wording.


>>Admittedly, there is another situation similar to the spoiler problem ---
>>the "center squeeze" scenario -- in which IRV may fail to elect the
>>Condorcet winner. In this scenario, the presence of a candidate with
>>strong core support causes a Condorcet winner with little core support to
>>lose. Fortunately, despite the theoretical possibility of this scenario,
>>the empirical evidence suggests that it is vanishingly rare in practice.
>>Despite the hundreds of public IRV elections that are conducted worldwide
>>every year, the actual concrete examples of it occurring in practice are
>>few and far between.
>
> A problem with using IRV elections to judge whether IRV suffers from
> a center squeeze effect, is that it overlooks the possibility that IRV's
> nomination incentives deter would-be Condorcet winners from running
> (due to the fact that everyone knows they would not win).

A fair point. I don't see it in practice, though. In the recent San
Francisco IRV elections, for example, there were three open seats
(incumbents weren't running). Two of the seats saw 9 candidates
running, one saw 7. It seems that everyone and their brother is
throwing their hat in the ring of these IRV races, with no sign that
centrists are being deterred by the voting method. I think the reason
that centrists aren't deterred is that they have nothing to lose --
the entry of a centrist with weak core support can't throw the
election to a less preferred candidate under IRV. The worst that can
happen is they're eliminated in an early round and then the tallying
carries on as it would have had they not entered the race. With
plurality, we see a very obvious nomination incentive, with potential
spoiler candidates publicly and explicitly dropping out of races,
because of the impact they may have. I've yet to see or hear of
anything comparable in an IRV race.


> You can make the argument that plurality also has very good Condorcet
> efficiency since it is never observed to fail to elect a Condorcet winner.
> Even adding the ability to rank lower preferences would probably not
> change this, since with no real change to the method there is also no
> real change to the nomination incentives.

While we don't have actual ranks to observe in plurality elections, we
still have pretty strong evidence, based on polling data, that
plurality has failed to elect the Condorcet winner in practice.


> I have a few problems with #4... Partly that I find the arguments
> speculative wrt candidate behavior, and partly that I don't see an
> inherent advantage in knowing where candidates stand if everything is
> still going to come down to competing blocs of core support that probably
> dislike each other. Mostly, and related, it's that if we agree that we
> can't trust voters to give us meaningful lower preferences, then I lose
> most of my enthuasism for voting methods. If we can only trust first
> preferences, and candidates that get a lot of first preferences, how much
> room do we really have to make improvements? We can stray from plurality
> hardly at all.

I trust lower preferences for candidates that exceed some threshold of
name recognition and exposure. That, for me, is where the benefit for
first preferences and "core support" come into play. They ensure the
candidate has at least some level of exposure.

Greg