On 05/28/2013 01:54 AM, Richard Fobes wrote:
On 5/27/2013 12:19 PM, David L Wetzell wrote:
...
The short-comings of IRV depend on the likely number of serious
candidates whose a priori odds of winning, before one assigns
voter-utilities, are strong. If real life important single-winner
political elections have economies of scale in running a serious
election then it's reasonable to expect only 1, 2 or 3 (maybe 4 once in
a blue moon) candidates to have a priori, no matter what election rule
gets used, serious chance to win, while the others are at best trying to
move the center on their key issues and at worse potential spoilers in a
fptp election.
Plurality voting and limited voting (and the Borda count if the voters
are undisciplined) are about the only methods that _cannot_ handle 3 or
(maybe) 4 popular choices along with any number of unpopular choices.
Don't forget IRV. If the three candidates are competitive, then IRV can
unpredictably fail due to center squeeze. That is what happened in
Burlington.
IRV works as long as the third party or candidate is small enough that
it couldn't possibly be a true center choice.
So it seems disengaged from reality to let C, the number of candidates,
go to infinity... and if a lot of candidates are not going to get
elected then to disregard voter info/preference over them is of much
less consequence.
Although the number of popular candidates is now small, that's because
we use plurality voting. When we use better voting methods, the number
of popular candidates will increase; of course not to infinity, but
frequently beyond the 3 or 4 popular choices that IRV can handle with
fairness.
Yes. That is also my point when I talk about "confusing p(multipartyism)
with p(multipartyism | dynamics given by plurality)".
Incidentally, if we generalize the effective number of political parties
formula of Laasko and Taagpera to "effective number of candidates", then
the mean effective number of political candidates in the Louisiana
gubernatorial elections, from 1991 to 20011 inclusive, is 3.5. Louisiana
uses delayed runoff. The maximum was 5.52 (in 1995); and this is in a
two-party environment. And already, even with the centralizing burden
imposed by two-party rule, the elections stray into the "multiple viable
candidates" territory where IRV may no longer be safe.
Although it's a non-governmental example, take a look at the current
VoteFair American Idol poll. The number of popular music genres is
about 5, and there are about 7 singers who get more than a few
first-choice votes.
http://www.votefair.org/cgi-bin/votefairrank.cgi/votingid=idols
IRV would correctly identify the most popular music genre (based on
current results), but probably would not correctly identify the most
popular singer.
That's not going to convince IRV promoters, since it's not a political
election. http://rangevoting.org/RangePolls.html may be better in this
respect. It gives results of Range and Approval-style polling for real
presidential candidates, and shows races where the polls say that other
candidates than the Plurality winner was preferred. For instance, McCain
was preferred to Bush in 2000, yet McCain lost in the primary.
And then you have other Range/Approval polls as well, like
http://rangevoting.org/PsEl04.html.
Now, one may claim that dynamics are not taken into account here. I
think that's a valid counter against Range as such (but others may
disagree). Yet if one starts involving dynamics, organizations that use
Condorcet don't seem to slide into two-faction rule; and the various
delayed runoff countries don't, either.
Why would voters trust a voting method that stops getting fair results
with so few popular candidates?
Yes, IRV is easy to explain, but that advantage becomes unimportant as
the number of popular candidates increases, which it will when better
voting methods are adopted.
I think that if we absolutely had to settle on a compromise, it'd
probably be Approval, which is a lot simpler than IRV. I don't like it
that much, since it encourages the voters to engage in what I called
"manual DSV". However, it's not as fragile as IRV, and the Range and
Approval advocates who don't like Condorcet can accept Approval.
I seem to recall someone saying that an informal EM poll picked Approval
as the CW. That's probably the reason, as I could easily imagine votes
going:
x: Range > Approval > Condorcet (Range advocates)
y: Condorcet > Approval > Range (Ranked ballot dudes)
z: Approval > Range > Condorcet (Approval advocates),
for comparable numbers x, y, and z.
But we don't have to settle on one compromise method. We don't have to
use Plurality logic to go beyond the problem of Plurality. That's what
the Declaration is all about; and the NZ referenda show that it's not
even necessary to use Plurality logic when asking the people what kind
of election rule to switch to.
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