[EM] Re : About Condorcet//Approval

[Kevin Venzke]

Hi Chris,

--- En date de : Jeu 23.10.08, Chris Benham <cbenhamau at yahoo.com.au> a écrit :
> Kevin,
> I think the version of  DMC  that allows voters to rank
> among unapproved
> candidates fails mono-raise, and both versions are
> vulnerable to Pushover
> strategy. 
>
> Would you say that that the plain "all ranked are
> approved" version
> doesn't properly fail mono-raise but instead fails
> mono-raise-delete?

I think it definitely fails the latter. I think it only fails the former
if you can't rank all the candidates (for approval purposes).

> http://lists.electorama.com/pipermail/election-methods-electorama.com/2007-March/019824.html
> 
> I wrote in March 2007:
> With the approval cutoffs, DMC  (and AWP) come close to
> failing mono-raise.
> 
> 31: A>>B
> 04: A>>C
> 32: B>>C
> 33: C>>A
> 
> A>B>C>A   Approvals: A35,  B32,   C33. 
> A eliminates (doubly defeats) B, and C wins. (AWP measures 
> defeat-strengths by the number of ballots on the winning
> side that approve the 
> winner and not the loser, and so says C's defeat is the
> weakest and so also
> elects C.)
> 
> Now change the 4 A>>C ballots to C>>A

To my mind you aren't allowed to move C over both A and the cutoff at
the same time, unless the method for some reason doesn't allow it any
other way (such as if this is the bottom of the ballot and you can't
approve all candidates).

Kevin Venzke