[EM] MCA and Approval strategy

[Kevin Venzke]

Gervase,

 --- Gervase Lam <gervase at group.force9.co.uk> a écrit : 
> > >  Would
> > > the voters use Approval strategy if normal Approval were used?  If so,
> > > they might do the same thing and vote for B as well as their favorite.
> > >  It really depends on what type of "Approval" strategy the voters in
> > > MCA and normal Approval use.
> 
> Sorry.  I rushed this paragraph a bit as it was late (Not that it is not 
> late right now!).  I pondered whether I should refer to the recent post 
> that Adam Tarr did on 26th April 2003 that clarified the main simple 
> Approval strategy.  I should have.

I read his message again.  It appears to be specific to the scenario that
there are no more than two viable candidates.  It's compatible with
Ossipoff's articles, which is the logic I was using in my reply.
 
> It is possible to come up with better strategies.  I think Mike Ossipoff 
> came up or tried to come up with a strategy that used win 
> probabilities/odds of each candidate to get the strategy.  I think the 
> overall feeling about this type of thing is that there is little gain for 
> a lot of effort.

http://electionmethods.org/Approval-1.html
If there are more viable candidates than ranks, I think it is useful.
Also, Ossipoff's strategies can be adapted to Condorcet with a fixed
number of slots.

> > The voters shouldn't approve B in plain Approval.  Pretty sure about
> > that. Their votes stand to gain them less if they do.
> 
> In addition to the main strategy, Adam also mentioned in the post: "If the 
> election is a dead heat between two frontrunners, the best strategy is to 
> approve candidates that you like more than the average of the two 
> frontrunners."

Here is my reasoning for why A supporters should not approve B:
Voter knows he is voting A>C.  Question is whether to vote A>B or B>C.
A's perceived odds = C's perceived odds.  (That's given.)
That means odds of A-B tie = odds of B-C tie.
That means B's perceived odds don't matter, only B's worth matters.
Breaking the A-B tie gains (100-15) or 85 worth.
Breaking the B-C tie gains (15-0) only 15 worth.
So an A supporter should vote A|BC.

I believe this would be Ossipoff's reasoning, too.

In Forest's Apr 19th message Forest refers to "Joe Weinstein's max
information strategy" where "each voter marks the approval cutoff so as 
to make the probability of one of the candidates above the mark winning as 
close to fifty percent as possible."  Using this strategy, you would decide 
whether to approve B solely based on B's perceived odds.

That's an odd strategy.  The mentality seems to be, "maximize the odds
that my vote will get me SOMETHING."

I'm having trouble even coming up with a zero-info strategy for MCA.
I think you would disapprove the same candidates as in zero-info Approval.
But what else?  You could
1. Mark "Favorite" all the candidates you approve, and leave "Approved" empty.
2. Mark only your Favorite "Favorite," everyone else is "Approved."
3. some mix, based on I don't know what.

It's very tricky because ranking A>B with A Favorite and B Approved does
not necessarily help A beat B.  It can KEEP A from beating B.

Kevin Venzke
stepjak at yahoo.fr


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