[EM] Condorcet strategy

[Dave Ketchum]

On Fri, 28 May 2004 08:20:13 -0400 James Green-Armytage wrote in part:

> 
> 	There are basically two things at issue.
> 1. How serious is the strategy problem in Condorcet? Is it serious enough
> to justify another balloting? Is it serious to render single-balloting
> Condorcet less stable than IRV?


Maybe "stable" needs fine tuning:

Assume:
      A ranks first or second on EVERY voter's ballot.
      Of candidates getting first rank votes, none get more than 49%, but 
others each get more than A.

Condorcet will recognize even this extreme, and A wins.

IRV will award to one of the other candidates with first rank votes (lower 
ranks can affect which of them).  Not seeing A unless a few voters change 
ranking qualifies as UNSTABLE from here.

Near ties can be thought of as unstable with either method, but are not 
something to be concerned about.  With Condorcet we talk of cycles in 
identifying a winner among some near ties, but still looking among those 
the voters most like.

SUMMARY:  No problem.
...

> 
> Sincere preferences
> 27: A>B
> 25: B>A
> 24: C>A
> 24: C>B
> Pairwise comparisons
> A:B = 51 : 49
> A:C = 52 : 48
> B:C = 52 : 48
> 	A is a Condorcet winner. But if just a fraction of the B voters reverse
> their preferences, they can steal the election for B. 


PROVIDED they have perfect information:
      To few and they get nothing.
      Too many and C wins - the voting pattern suggests this would be a 
catastrophe and whoever proposed it better hide in a hole.
...

> 
> Dave Ketchum wrote:
> 
>>If this argument managed to kill Condorcet, 
>>
> 
> 	This is definitely not my intention.


And whoever took their eyes off the road to use a cell phone had no bad 
intention to kill an accident victim - we need to think on expectable 
results of our actions.

> 
> Dave Ketchum wrote:
> 
>>Conceded that a private group might contain the ability and willingness 
>>for strategies of this sort, public elections have to be about immune.
>>Potential strategists have to predict the expectable results with no 
>>effort and what effort will promote a better result without going into 
>>something worse.
>>

See my note above.

...
> 
> Adam Tarr wrote:
> 
>>I see it as extremely unlikely that burial strategy would 
>>be successful on a large scale without public coordination, which would
>>be 
>>easy to counter and would create a big scandal.
>>
> 
> 	This is one of my newer points. I don't think that coordination is
> necessary. As long as voters understand the system, and are aware that
> strategy can bring both risk and a possible advantage, I think that they
> can make up their minds individually when they go to the ballot box. 
> 

Again, they need to consider possible harm - difficult without knowledge 
and coordination - and difficult to coordinate without alerting enemies.
...

> 
> Mike Ossipoff wrote:


Thanks, Mike, for writing in detail separately.
...

> 
> Sincerely,
> James

-- 
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  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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