[EM] Real IRV Election, Disputable Result
jlundell at pobox.com
Sun Mar 12 12:24:01 PST 2006
At 1:57 AM -0700 3/11/06, Jan Kok wrote:
>I crunched the election data and found that Kiss was preferred to
>Miller, 4755 to 3988.
That's still not numerically consistent with the published Burlington
results; I wonder what the discrepancy is.
Let me dispute your "drat", though. Your thrust, I suppose, is that
you'd like to find an IRV election in which there was a Condorcet
winner not elected by IRV. I suggest that this quest is based on a
fallacy, and that such a result could not legitimately be used to
argue the merits of IRV vs Condorcet ranking.
I'm not arguing the merits of IRV vs Condorcet here; I go back and
forth on the question myself. I'm only arguing against the validity
of a particular sort of evidence.
The fallacy lies in different voter behavior. IRV and Condorcet
ranking come with different guarantees to the voter. An example (and
there are examples on both sides) is that IRV guarantees
later-no-harm. That is, the IRV voter can freely rank lower choices
with the assurance that those choices cannot harm the chances of the
voter's earlier preferences.
Condorcet ranking does not (and cannot) make that guarantee. So the
same set of voters (in Burlington VT, say) faced with the same
candidates but a Condorcet rather than an IRV election, are likely to
cast different ballots. So to take an election profile that was made
under IRV rules and apply Condorcet ranking to it might be of casual
interest, but it's an apples and oranges comparison.
I'm not claiming that later-no-harm is a decisive argument in favor
of IRV; Condorcet ranking has its own advantages, and later-no-harm
is not IRV's only advantage. I'm only arguing that you mustn't change
the counting rules after the election without also giving the voters
a chance to change their ballots in view of the alternate rules.
All this is further complicated, of course, by the fact that voters
are human, and are neither perfectly informed nor perfectly rational.
But they're somewhat informed, and somewhat rational, and we must
expect that the specific election rules in place will have some
effect on voter behavior.
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