We know that Plurality has problems - and go to great effort to find
something better.
If IRV functioned like Plurality, that would tell us IRV is not the
magic improvement desired.
IRV is different - which could give us hope for being better. There
are demonstrations showing success - and too many showing that IRV
fails to fulfill that desire. Here Warren offers detailed analysis of
that failure.
For voting IRV has advantages - the voter can indicate which
candidates are seen as better than others. Minor lack that no two
candidates may be assigned the same rank. Regrettable that magnitude
of differences cannot be expressed BUT, this means no responsibility
for being consistent with other voters as to magnitude.
Vote counting is IRV's major weakness, discarding by formula some top
most ranks from some ballots, counting resulting top ranked
candidates, and never seeing what voters may have ranked below these.
The formula also requires going back to ballots as part of each step
in discarding.
On Aug 27, 2010, at 11:32 AM, Warren Smith wrote:
Re: [ESF #1563] Instant Runoff Voting 3-candidate elections -
pathologies considerably more common than you may have thought
http://rangevoting.org/IrvParadoxProbabilities.html
computes the probabilities of a lot of pathologies in IRV3.
It is, I believe, the best available such computation.
The "total paradox probability" in such elections, i.e. the
probability that at least one among the 8 pathologies {Q, R, U, V, W,
X, Y, Z} occur in a random election, is found to be
24.59%, 13.98%, and 27.50%
in our three different probability models. But if we restrict
attention to elections in which the IRV process matters, i.e. in which
the IRV and plain-plurality winners differ (i.e. exactly the elections
IRV-advocates tend to cite as examples of the "success" of the Instant
Runoff Voting process), the total paradox probability becomes
stunningly large:
74.10%, 72.61%, and 54.44%
For the most part, this was not previously recognized. This goes a
long way toward explaining why it has been so incredibly easy for
people like me to find pathologies in real-world IRV elections,
seemingly most of the time we ever looked at any interesting IRV
election for which we could obtain enough data, and seemingly
especially in the elections cited by IRV-advocates as "great
successes" for IRV.
It is reasonable, in the face of such massive and frequently-arising
evidence that IRV has (obvious) problems, to promote it, as opposed to
some simpler method largely free of such problems?
Two details about this last paragraph continue to amaze me:
That Warren would not have noticed and amended it.
That the many other readers would see no problem worth reporting.
I keep wanting to replace "is" by "is NOT"!
--
Warren D. Smith
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