[EM] IRV in action

[Dave Ketchum]

On Wed, 09 Apr 2003 11:33:41 +0200 Markus Schulze wrote:

> Dear Dave,
> 
> you wrote (9 April 2003):
> 
>>Markus wrote (7 April 2003):
>>
>>>Example:
>>>
>>>  40 voters vote X > Y > Z.
>>>  35 voters vote Y > Z > X.
>>>  25 voters vote Z > Y > X.
>>>
>>>  Candidate Y is the IRV winner.
>>>
>>>  Suppose that candidate Z asks his supporters to bullet vote.
>>>  Then this example looks as follows:
>>>
>>>  40 voters vote X > Y > Z.
>>>  35 voters vote Y > Z > X.
>>>  25 voters vote Z.
>>>
>>>  Now candidate X is the IRV winner. Now candidate Z can hope
>>>  that some of the supporters of candidate Y will give their
>>>  first preference to candidate Z to keep candidate X from
>>>  winning. Then this example looks as follows:
>>>
>>>  40 voters vote X > Y > Z.
>>>  35 voters vote Z > Y > X.
>>>  25 voters vote Z.
>>>
>>>  Now candidate Z is the IRV winner.
>>>
>>How did we get here?  We started with Z voters liking Y better than X.
>>Why would they destroy that via bullet voting?
>>How did this ever happen?  After the Z voters make sure Y could not win,
>>what kind of arm twisting is ever going to get Y voters to help Z win???
>>
> 
> Of course, strategical behaviour is something subtle. The party of
> candidate Z will say: "Use bullet voting to demonstrate that when Z isn't
> elected then it doesn't matter who is elected." This party won't say:
> "Use bullet voting to keep Y from winning."
> 


Leaves me suspecting it may be too subtle to work.

We start with Y and Z being siblings, such that neither wants X to win, 
but Z predicted to be weaker than Y.

Now you claim:
      Z can get the Z voters to bullet vote, leading to X winning unless Y 
voters give up on their candidate and vote for Z.
      Y voters will agree.

Smells, as I said above.  That Z is promising to make sure Y cannot win 
CANNOT make friends.  Y's proper response is to tell Y voters to ignore 
this nonsense, for Z has demonstrated being less qualified by this tactic, 
and to tell Z voters to vote normally because what Z is promoting is not 
going to work.

> Markus Schulze

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