Optional Preferential Voting and the 2010 election

Rod Hagen on Pollbludgers mentioned an article by Mumble

Rod pointed out that Mumble had claimed that
Optional Preferential Voting (OPV) would have delivered Australia
to Abbott in the 2010 election.

However, you pointed out that OPV might not be so bad for
the ALP as 1) more of the currently informal votes that
would become formal would favour the ALP and
2) the Greens would generally be more careful to make sure that
they indicated their preferences among the major parties.

You said that Mumble disagreed.

So, I had a look. I took the results of the vote across the country
and plugged them in with a couple of adjustments to
take account of your model of OPV. In particular I gave
the ALP 2% of the 5% informals and the LNP 1%.
I also assumed that 80% of the Greens would indicate
their preference ALP or LNP. I assumed that only 50%
of the minor party and independent voters would
indicate their preferences.

What are the results of this simulation?

All the 4 independents and Bandt and Crook still win.

141 of the other seats turn out exactly the same.

Only three seats change winners under OPV.
They are:

Forde gets won by the ALP instead of LNP.

Herbert gets won by the ALP instead of LNP.

Hasluck gets won by the ALP instead of LNP.

So I’m with you Rod. Under reasonable assumptions
on the effects of OPV, the ALP wins 3 more seats.

Final result. ALP 75 seats, Green 1, Inds 4, NatWA 1,
Coalition 69.