University of Auckland says:

Dr Geoffrey Pritchard and Dr Mark C. Wilson, members of the Centre for Mathematical Social Science at the University of Auckland, have created a simulator intended to voters to compare the 5 proposed electoral systems in a quantitative way, by allowing them to compute quickly, for a given polling scenario, the party seat distribution in Parliament under each system.

The simulator is here.

Its a useful resource, and it is great they have provided it. However it is also a good example of the difficulties you can get when you take an academic approach to an issue, rather than a more practical approach.

This is best shown by way of example. The simulator predicts that the 2002 election, if held under FPP would have had a result of 110 seats for Labour and 10 for National.

Now in 2002 National actually won 21 electorate seats out of 69 or 70. So this model is saying if there were 50 extra electorate seats, National would win 11 fewer seats!!

Why? Because they have come up with a formula based on the last 50 years or so of FPP elections, which they applied to the party vote figures for 2002. They ignored the actual electorate vote. It is a classic academic approach.

The more pragmatic approach, which is what others have done, is to say well if National won 21 electorate seats in 2002 out of 70, then if there 120 seats, their estimated number of seats would be 21*120/70, which is 36 seats.

For the same reasons, the model doesn’t predict the Maori Party would have won any seats in 2008 under FPP (as they had a low party vote), even though the Maori Party won 5/7 Maori seats, and hence if there were 12 Maori seats, one would expect they might have won 10/12, not 0/12.

So it is a useful resource, but it should not be treated as particularly authoritative in terms of alternate scenarios. Of course no alternate scenario is ever authoritative.