On 05/27/2013 09:19 PM, David L Wetzell wrote:
Smith's http://rangevoting.org/PuzzIgnoredInfo.html
needs to be taken w. a grain of salt.
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.
That argument is too strong in the sense that it can easily be modified
to lead to any conclusion you might wish. And it can be modified thus
because it is too vague.
Let me be more precise. You may claim that if there're some economies of
scale, then it's reasonable to only expect 1, 2 or 3 viable candidates.
But here's a problem. Without any data, you can posit that the economies
of scale kick in at just the right point to make 2.5-party rule
inevitable even under Condorcet, say. But without any data, I could just
as well posit that the economies of scale, if any, kick in at n = 1000;
or, I could claim that the economies of scale kick in at n = 2 and thus
we don't need anything more than Plurality in the first place[1].
So one may claim that "important single-winner political elections"
necessarily have economies to scale that make anything beyond 2.5-party
rule exceedingly unlikely. But without data, that's claim isn't worth
anything. And without data that can't be explained as confusing
P(multipartyism) with P(multipartyism | political dynamics given by
Plurality), the simpler hypothesis, namely that there is no such barrier
that we know of, holds by default.
And, if you're not claiming that there is such economics of scale, but
simply that there *might* be, then it's still less risky to assume
multipartyism is right and use an advanced method. If we're wrong,
nothing lost but "momentum". If we're right, we avoid getting stuck at
something that would still seriously misrepresent the wishes of the people.
(I'd claim, based on (among other things) international data under
Runoff, that there's little evidence that multipartyism is inherently
incompatible with single-winner rules in general. But such data can
easily be specially pled away by making the rules about what counts
circuitous enough. So if I'm going to go in that direction, I'd like to
have some idea of, before the fact, what kind of evidence will convince
and what will not.)
[1] Possibly with stricter rules to entry so that insignificant third
parties don't spoil the elections. Adding such rules, e.g. requiring
more signatures for candidates to run, would be a lot simpler and less
expensive to implement than switching to IRV.
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