First of all, let's take alternative vote versus first past the post. In many respects, these are going to be very similar systems in terms of their aggregate results because they have a district magnitude of one. If you look at the history of the Australian state and federal elections, you're going to find that the alternative vote generates a fair amount of disproportionality simply because of that district magnitude of one. However, you're also going to have a little more room for independents and smaller parties to get in on the basis of preferences. There are some arguments that centrist parties, parties that are positioned to capitalize on second preferences, do better under that sort of system. If you look at the Australian experience, the Labor Party sees itself as a right against two centre-right parties, and it gets power sometimes and gets to effect its agenda.
With respect to first-past-the-post and mixed systems, I think what we need to understand about the mixed member proportional system is that it is a proportional representation system. The district level representation is peripheral or subordinate to the proportional representation element.
Mixed systems are motivated by the idea that we can get the best of both worlds—we get a proportional result and we get local representation. I think they've been tried with, as I would expect, various results around the world. The German experience has been largely positive. The New Zealand experience has been, on the whole, satisfactory, although with different people complaining about different aspects of the system. The one aspect that gets on people's nerves a bit is the issue of dual candidacy. Here, if you lose an election, you lose an election. When you have dual candidacy, the members are allowed to contest the district and the list, and this can almost always ensure their election or at least insulate them from defeat. My reading of this is that it has gotten on people's nerves in New Zealand, but it's not a huge problem.