[EM] 'Turkey' problem, manipulability

[Kevin Venzke]

 --- Alex Small <asmall at physics.ucsb.edu> a écrit : 
> MCA is also more likely to elect A in this scenario.  The A>B>C faction
> can safely rate A preferred and B acceptable, unless they believe a
> majority of the electorate is rating both B and C as preferred.  So while
> MCA is not completely immune to manipulation of polls (is anything?), it's
> certainly more robust than some methods.

Looks that way.  A supporters who think A could have a majority might even
disapprove B.  However, if they think C might have a majority of "preferred"
ratings, they might bump B up to "preferred" along with A.  This scenario 
seems more likely than what you envisioned.

> Also, can somebody remind me what the "Turkey Problem" is?  This thread
> has been going on for a while.  I seem to recall it having something to do
> with a candidate winning even though a lot of people didn't really like
> him that much.

It's just what you say.  The context was specifically Condorcet.

I think the topic is dead, though, unless someone has something new to
add...

> Alex

> Forest Simmons said:
> > See the full text of message 10396 for further analysis showing that
> > Borda and IRV are also apt to give B the win in this context, while
> > Condorcet and Candidate Proxy are almost sure to elicit more sincere
> > votes and give the win to A.

That's a great post.  Thought-provoking.

I want to consider the case with three-rank Conditional Approval (of interest
only to me, perhaps):

Sincere:
6000 A>>B>C
3000 C>B>>A
1000 B>C>>A

False poll:
35% A>B>C
40% C>B>A
25% B>C>A

Believing these poll results, the A supporters have no reason not to
vote A|B|C.  Why?  They only end up supporting B if C takes the lead.  They
don't risk keeping A from beating B in this way, because they don't believe
any of the B/C voters are willing to compromise on A.  So the thought is,
if C leads, A is no longer viable, so why not support B.

The strategy of B and C voters is more complicated, but it doesn't make
a difference in the outcome.  The results would be:
6000 A|B|C
3000 C|B|A or C||BA
1000 B|C|A or B||CA

A is the initial leader in any case.  In response, B and C can't get
any more than 4000 votes total.  Thus A remains the leader and wins.


Question: What advantage does MCA have over three-rank Condorcet?


Kevin Venzke
stepjak at yahoo.fr


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