[EM] IRV vs Condorcet vs Range/Score

[Aaron Armitage]

--- On Mon, 10/13/08, Chris Benham <cbenhamau at yahoo.com.au> wrote:

> From: Chris Benham <cbenhamau at yahoo.com.au>
> Subject: [EM] IRV vs Condorcet vs Range/Score
> To: "EM" <election-methods at lists.electorama.com>
> Date: Monday, October 13, 2008, 11:35 AM
> >CB: Not necessarily, no. I have in mind something like
> >(with sincere ratings):
> >
> >49: A(99)  > C(2)  > B(1)
> >48: B(99)  > C(2)  > A(1)
> >03: C(99) > A(98) > B(1)
> >
> >C is the CW, but A is a much more stable, much higher
> SU,
> >arguably as fair or fairer winner.
> >
> 
> Aaron Armitage wrote:
> Any strategically informed voter will give approval-like
> ratings, and will
> approve the top two frontrunner he likes better, as well as
> any candidates
> he prefers to that frontrunner, which means that the stated
> ratings will
> look like that regardless of the real ones and a range
> election will tend
> to produce that result regardless of how much utility
> voters attach to
> each candidate. And, of course, IRV produces the same
> result.
> 
> What you're suggesting, then, is a case where the
> sincere ratings just
> happen to match the stated ratings that would be produced
> by strategic
> voting, and that in this special case the strategic voting
> under range or
> approval will look legitimate in elected A over C despite
> the existence of
> a majority coalition for C over A. But range and approal
> must assume that
> this is always the case, when it almost never is.
> 
> CB: I explicitly specified that the ratings are sincere.
> You seem to be assuming
> that I am promoting Range or Approval as better than all
> the Condorcet methods
> when I am not. I just gave the example to show that the
> sincere CW isn't necessarily
> the most stable or only justifiable winner. (Maybe I am in
> the wrong thread.)
> 

Yes, I know you stipulated all the preferences were sincere. That's part
of what makes your scenario tailor made for range and approval systems. It
shouldn't be surprising that range and approval work well in cases
specifically designed for them.

> Since all Condorcet methods fail Later-no-Harm, in practice
> in a Condorcet election
> the A and C supporters would most likely truncate making A
> the voted CW. If only
> the A supporters truncate then the candidates are in a
> cycle that would most likely
> be resolved in favour of  A.
> 

I had thought of making this point, but you could just as easily stipulate
that voters are required to rank all preferences. This is a good reason
truncation should always be allowed.

In general, the "core support" argument misses a crucial point: recruiting
campaign staff and volunteers resembles plurality and fundraising
resembles (sincere) range, except without the equality inherent in formal
voting. A candidate that hardly anybody likes won't be running a strong
enough campaign for more mainstream voters to even know who he is; their
truncation is less likely to be a strategic countermove than a simple
expression of ignorance. FairVote's boogeyman, a CW with no first
preferences at all, cannot happen because unless he was his own first
preference he wouldn't run.