[EM] In political elections C (in terms of serious candidates w. an a priori strong chance of election) will never get large!

[Kristofer Munsterhjelm]

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.