[EM] IRV in action
Markus Schulze
markus.schulze at alumni.tu-berlin.de
Tue Apr 8 03:10:01 PDT 2003
Dear Dave,
I 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.
You wrote (7 April 2003):
> Given the candidate's positions being equidistant:
> IRV - I see not how bullet voting matters, for nothing else is seen
> until/unless your candidate loses.
>
> Given two candidates being siblings, far from the third:
> IRV - voters for a sibling candidate almost certainly want to give
> the other sibling second preference, to decrease the chance of the third
> candidate getting elected. I would expect these two candidates to promote
> this voting. I do not see the third candidate caring, as I said above.
Suppose that there are three potential winners: X, Y, and Z.
Suppose that Y pairwise beats X when every voter votes sincerely.
Suppose that Z pairwise beats X when every voter votes sincerely.
Suppose that Y cannot pairwise beat X without the votes of the Z supporters.
Then it makes sense for the Z supporters to bullet vote so that the
Y supporters see that Y cannot win. At least those Y supporters who
have Z as their sincere second preference will then give their first
preference to Z so that Z wins.
Markus Schulze
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