[EM] Re : About Condorcet//Approval

[Chris Benham]

Kevin,
I've always thought that the main value of  mono-raise is that methods that fail it are 
vulnerable to Pushover strategy and those that meet it aren't. 

push-over 
The strategy of ranking a weak alternative higher than one's preferred alternative, which may be useful in a method that violates monotonicity.
http://condorcet.org/emr/defn.shtml

But now you are proposing an interpretation of  mono-raise (aka monotonicity) that can 
be met by a method that is clearly vulnerable to Pushover strategy.
 
25: A>B
26: B>C
23: C>A
26: C

What is the value/use of a criterion that does that and moreover can be met by a method
that fails to elect C in the above election?   
 
The method under discussion that you say meets mono-raise, Definite Majority Choice
(Whole), elects B.
 
 
All candidates are in the top cycle, but by our 3-slot ratings ballot interpretation C has
the highest TR score, the highest  approval score, and the lowest approval-opposition
score.
 
Would you agree then that there is a need for an  "Invulnerability to Pushover strategy"
criterion, that is more important than mono-raise?
 
Chris Benham
 

 

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

I misstated something:

--- En date de : Dim 26.10.08, Kevin Venzke <stepjak at yahoo.fr> a écrit :
>> 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).

You can move C over both at the same time, but you can't, at this same
time, move A and the cutoff relative to each other, according to my
opinion.

Kevin Venzke


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