The AEC has released the preference distribution data from the election, so it’s worth having a bit of a squiz at the way preferences flowed from the Greens to the ALP, as there’s some interesting little bits in there. To start with, it’s worth looking at the broader picture on the vote side – so […]

The AEC has released the preference distribution data from the election, so it’s worth having a bit of a squiz at the way preferences flowed from the Greens to the ALP, as there’s some interesting little bits in there.

To start with, it’s worth looking at the broader picture on the vote side – so the primary vote and the primary vote swing for the Greens and the ALP, by state and territory, came in like this:

That gives us a bit of a feel for the results – so in places like NSW we had the swing away from the ALP being much larger than the swing towards the Greens, while in places like Victoria we saw the opposite occur, where the swing to the Greens was much larger than the swing away from the ALP.

So we have a pretty non-uniform result across the States and Territories in terms of the magnitude of the Greens picking up votes at the net expense of Labor.

On the preference side of things, the flow of Greens preferences to the Labor Party at the national level reduced by nearly a point, from 79.96% at the 2007 election down to 78.84% in 2010. If we break those Greens-to-Labor preference flows down to the state and territory level, we find that only the NT had a particularly large change – with flows dropping by 4.3% since the last election:

NSW is an interesting case, where not only did the ALP take a pretty big hit on their primary vote, but the preference flow from the Greens to the ALP also dropped – suggesting that the ALP really was quite on the nose and not just suffering a protest vote from the left end of the spectrum.

In terms of the two party preferred, we can look at how many points of ALP two party preferred that Greens voters ultimately delivered to Labor at the election.

What we find is that Labor experienced an increase in the number of points of two party preferred that the Greens gave them in every State and Territory – though with quite a bit of variance. In NSW, the Greens gave Labor an increase of 1.7 points over the 2007 election result, while in the ACT it increased by 5.3 points.

The headline numbers are also quite interesting, with Greens voters in Victoria, WA, Tassie and the ACT now all delivering the ALP double digits worth of two party preferred. This is important mostly for “stating the obvious” type reasons – the Labor party is becoming more reliant on the Greens delivering them the ultimate post-preferences vote they need to win seats.

This raises a couple of questions. Firstly, how many seats did the Labor party win because of Greens preferences?

The answer here is easy – out of the 72 seats Labor won, 48 of those were reliant on Greens preferences for victory.

The second question is a bit trickier: What effect on Greens preference flows did Greens HTV cards have?

To answer this, we can do some regression work. Firstly, we need data on the electorates where the Greens preferenced Labor over the Coalition compared to where they didn’t run a recommended preference flow on their local HTV cards. We can get all that from here.

Next, we need preference flows by electorate, which the AEC kindly provides here. We can’t use all 150 electorates here as there were some issues in some electorates which distorted things slightly – so if we use only those electorates where the final two candidates were Labor and Coalition (removing the issues), that gives us 142 seats worth of data to look at.

If we regress the Greens-to-Labor preference flows by electorate against a dummy variable which represents those electorates where the Greens preferenced Labor on their HTV cards (96 of those 142 electorates), we find that the existence of a Greens How To Vote card preferencing Labor increases the Greens to Labor preference flows by an average of 3.3%.

But, that’s not the full story. One of the issues here is that the preference flow rate is correlated with the size of the Greens primary vote in such a way that for every 1% the Greens primary vote increases, the preference flow to Labor increases by around 0.6% – presumably as that increase comes from people voting for the Greens that would ordinarily be Labor voters. So once we control for the size of the Green primary vote, what we end up with is this (a cut and paste from the stats software):

For every 1% increase in the Greens primary vote, preference flows from Greens to Labor increased by around 0.6%. Holding that constant, what we also find is that the existence of a Greens HTV card preferencing Labor increases that preference flow rate by 2.71% These results are highly statistically significant.

Also worth noting is that I checked for a donkey vote effect in a number of ways (to make sure that any donkey vote wasn’t distorting the relationships were looking at here) and there wasn’t one that was even remotely close to being statistically significant.

What do these results mean in practice?

Well, let’s take the tightest ALP win at the election in the seat of Corangamite as an example. Here there was a Greens HTV card preferencing Labor ahead of the Liberals and the result was a Labor two party preferred result of 50.41% to the Libs 49.59%, or 47,235 votes to 46,464 – a Labor lead of 771 votes.

Greens preferences in Corangamite flowed to Labor at a rate of 80.31% (while the broad “Others” flowed to Labor at 41.92%). If the Greens didn’t have a How To Vote card that preferenced Labor, we would expect that the preference flow rate would have dropped by around 2.71% – bringing the Greens preference flows to Labor down to 77.6%.

With that 77.6% Greens preference flow, Darren Cheeseman would still have won Corangamite for Labor by 50.1% – or around 190 votes.

As that was the closest Labor seat, there was no seat in the country where the size of the average Greens HTV card effect was larger than the Labor Party’s winning margin –which really is quite interesting.

That’s not to say that Greens HTV cards didn’t deliver Labor some seat, somewhere -just that if such a thing did occur, it was more a result of fortuitous local variation than any broader, nation wide HTV card effect.

Greens voters, on average, didn’t appear to pay a great deal of attention to their party’s How To Vote cards.

Then again, they rarely do.

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