[EM] IRV in action

[Markus Schulze]

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."

Markus Schulze