Saturday, 28 August 2010

Can it be fair that the person third in the first round goes on to win under AV?

There has been a bit of fuss over one of the results in the Australian election that was held under AV.

http://blogs.abc.net.au/antonygreen/2010/08/distributing-preferences-in-denison.html

The key part of this is that the person who came third in the first count (Wilkie) went on to win!


Jackson (Labor)35.9%
Simpkins (Liberal)22.1%
Wilkie (Independent)21.7%
Couser (Greens)19.0%

Some people said this had to be unfair as Jackson and Simpkins seemed so much more popular.

However what actually happened is that Couser was knocked out and almost all of his voters had put Wilkie as next choice. This put Wilkie up from third into second place, so Simpkins was knocked out next. Once his supporters next choices were counted up Wilkie was in first place with over 50% of the votes and so Wilkie won.

Realistically, under First Past the Post, the result would almost certainly have been the same!

This is because in FPTP the greens would have realised that they had no real chance, so voting green would let Labour win. Accordingly they would have voted tactically and voted for Wilkie in the first place!

So the result is probably the same, in which case what is the advantage of AV?

Well the advantage of AV is that looking at the first preferences (above) we know the true level of support for each party - the greens have 19% and keep their deposit, and Wilkie knows that many of the votes that got him in belong to Green supporters.

Under FPTP the result would be the same, but the Greens would probably have (unjustly) lost their deposit, and Wilkie would not have realised how many of his votes were from people who were really Greens.

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