[Way OT] Condorcet vs. IRV (was [Slightly OT] Re: Voting)

Joe Mason joe at notcharles.ca
Thu Mar 25 21:14:36 CET 2004


In article <1gb7bj1.xgiqcjp3ro1iN%egusenet at verizon.net>, Eric wrote:
> Yes, I understand this is the claim that some IRV proponents would make.
> However, no such definitive statement can honestly be asserted based on
> those ballots. With most (if not all) ranked ballot methods (including
> Condorcet and IRV), if a voter truly does not want a Candidate to win,
> the way the indicate that is by leaving that Candidate unranked.
> 
> In this case, the A & B voters did not leave C unranked. Both groups
> clearly stated that they preferred C to their primary opponent.
> 
> What we do not know, because neither IRV nor Condorcet collects the
> strength of the preference (there are inherent problems with doing such
> a thing which is beyond the scope of this message), is how strong the
> preference is for the A & B voters for C rather then their primary
> opponent.

Well, not too much beyond: the inherent problem that I know is that
there's no incentive to put anything other than 100 or 0 to maximize the
strength of their vote.  (After all, if you prefer A to C by 100 to 99,
but putting that you prefer it by 100 to 1 will get A elected, why not
do it?  Lack of perfect information makes this kind of strategic voting
dangerous, but that doesn't mean people won't try it, and that
destabilizes elections.)

> For example, it could be that:
> (The numbers in parenthesis indicate the strength of how much the
> candidates are liked on a linear 0 - 100 scale)
> 
> 49 A(100) > C(99) > B(0)
> 48 B(100) > C(99) > A(0)
> 3: C(100)
> 
> Should this be true, one would be hard pressed to develop a credible and
> compelling argument that C should not be the winner.
> 
> However, it is also possible that:
> 
> 49 A(100) > C(1) > B(0)
> 48 B(100) > C(1) > A(0)
> 3: C(100)
> 
> In which case, an argument can be made that C should not be the winner.
> 
> But, like I stated, neither IRV nor Condorcet collect such information,
> so, what is the fairest way to deal with this?

One interesting approach was brought up on the elections list just
before I stopped reading it.  (Wait, don't I recognize your name from
there?  You'd be more familiar with it than I, but I'll bring it up
anyway, on the assumption that there are other interested readers out
there.)

Add an implicit "none" candidate to separate rankings of actual
preferences from least of the evils.  Your first case becomes "A > C >
none > B", and the second (probably) "A > none > C > B".  So in the
latter case, the voter is saying that they prefer C to B, but only if
forced to choose between them due to overwhelming preference by the rest
of the electorate.

I'd be grateful if you can point me to a thorough analysis of this idea,
since it sounds reasonable to me but I don't really have the background
to evaluate it.

> With IRV, if your top choice is eliminated, your second choice is
> automatically promoted to a strength of 100, regardless of how you
> actually feel about that candidate. For example, say a voter had voted
> (I've included theoretical preference strengths):

Ah, thanks for pointing that out.  I knew it sounded a little fishy.

(So much nicer to have nobody from the other side cluttering up the
debate...)

Joe



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