Jameson Quinn wrote (23 July 2010):
In Australia (IRV), the clear strategy is to vote in a plurality-like way.
That is, between two near clones A and B who share a majority, supporters of
A, the one with least support from C voters, should betray and vote BAC. In
the absence of such a strategy from A voters, C voters should dishonestly
vote CAB, under the assumption that BCA and ABC are more common than BAC and
ACB. Both of these strategies are simple enough to describe, especially if
there's a pseudo-one-dimensional issue space. The favorite-betrayal one, if
correctly applied, increases social utility and would probably dominate and
suppress the burial strategy (since it's an effective defense). But as we
can see with plurality, it also decreases incentives for conciliation from
candidate B towards the A voters, allowing party B to become more corrupt
over time.
Jameson,
What exactly do you mean by the phrase "share a majority"?
I assume that in your scenario there are only three candidates. Is that
right?
IRV is invulnerable to Burial strategy, and meets Majority for Solid
Coalitions.
If the A and B supporters (a majority of the voters) all vote both A
and B above C then C can't win.
But if they don't then it is the supporters of the member of the pair of
near-clones with the least support from the other
one that has the incentive to "betray" their favourite by using the
Compromise strategy.
49: C>B
21: A>B
03: A
27: B>A
Of the A-B pair of "near clones" it is A who has the "least support
form the C voters", but it is the supporters of B with
the incentive to betray by Compromising.
Chris Benham
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