Oops, a typo. 11.5 and 12.5 should have been 10.5 and 11.5.
Anything between 5 and 14%, I would think. I was expecting a swing of around 17%. The low voter turnout likely helped the Liberals, as did the informal votes. I'd suggest the real swing, as it stands at present, is hovering around 11.5-12.5% - not great, but certainly tolerable. Hennessy will have to work hard to rebuild Kosky's former support, but she's likely to manage it.
The preference flow is quite amusing, really. It's a way of making more work for the counters:
Greens -> SA -> (Greens) -> Labor
But, of course, one begins with the SA:
SA -> Greens -> (SA) -> (Greens) -> Labor.
All three remaining booths traditionally strong labor.
The lack of support for the green candidate is both interesting and troubling. They spent a good deal on their campaign - indeed, it has been a focus of the party for some time - and campaigned on issues important (at least, according to the polls) to the local electorate. Perhaps it's simply a sign of the true strength of the Labor base? Perhaps those who, in other electorates, would have voted Green simply filed informal ballots rather than betray their party? Of course, this is all merely speculation.
Further, I'd suggest the informal vote, rather than being solely a reflection of the dullity of the by-election (though it does figure, of course), is rather more the result of universal dissatisfaction causing apathy.
I agree with Alex that this by-election can't be extended to the polls later this year, however I differ on reason. Much of the swing can be put down to a new candidate replacing a previously powerful one, and the laziness of the ALP campaign team - very few resources were dedicated to this electorate (presumably keeping the war chest for the next full election) and I think that's reflected in the results, especially in the outer booths.
The green's public transport campaign was probably one of the more effective we've seen from the minor parties in some years. Indeed, this could be a great upset and go the way of Fremantle, though it is admittedly unlikely.
I should have mentioned Labor holds this seat by a margin of slightly over 20%. 2009 was, of course, a dismal year for Labor in the state, and the backlash from the electorate at this election, and presumably the next state election, is likely to be great