ALP two-party preferred vs 1st preferences

Tuesday October 8, 2013

Filed under: Australian Politics — jackman @ 2:39 pm

[Update: Let’s try this again…after Kevin Bonham pointed out that I’d screwed up some of the computation here]

I was inspired to make the attached graph after seeing some of Mumble’s tables (Mumble now has a table directly on this topic).

I plot ALP two-party preferred (vertical axis) against ALP 1st preferences (horizontal axis); see the in-line PNG below or this PDF in a separate browser window. The raw data are available in a table, CSV or as a RData object.

Keep in mind that we’re still waiting on TPP counts in 11 of the 150 seats in the House of Representatives, but that won’t change the big picture.

Some commentary below.

ALP two-party preferred vs 1st preferences, by electoral division

Note immediately that Labor won just one seven seats with a clear majority, without going to preferences; these are labeled on the upper right of the graph. It is interesting to see McMahon in this set, a seat which was thought to be part of the anticipated Western Sydney Labor wipeout at one point. I’m sure other commentators have noted this, but it is rather striking, a reflection of just how poorly Labor performed on 1st preferences in 2013.

Labor did not win more than 50% of 1st preferences in any of the seats yet to report a TPP count (and so not displayed on the scatterplot). Labor’s 1st preference performance in these seats ranges from 11.7% (Indi) to 45.1% (Wills).

The flow of preferences to Labor (inherent in the definition of two-party preferred) means that ALP TPP > ALP 1st prefs, in every electoral division, and so the data lie comfortably above the diagonal, 45 degree line. The dark line is a smoothing spline, that is pretty much linear, save for the kink around 46% ALP 1st preferences.

That is, preferences are flowing to Labor pretty much proportionally to their 1st preference vote share, at least on average. In fact, the linear model ALP TPP = 95% of ALP 1st prefs + 14 isn’t a bad approximation (OLS, r2 = .90), save for a few seats.

I’ve labelled some cases where Labor TPP is considerably higher than we’d expect given the 1st pref result: e.g., Grayndler, Gellibrand, Sydney, Melbourne Ports and Richmond. Unsurprisingly, these are all seats where the Green vote was quite strong.

Grayndler, Gellibrand and Sydney are seats where Labor polled 43% to 44% on 1st preferences, the Green result ranged between 16% and 21% (way above the Green’s national vote share), and/or (a) the vote for other minor parties was low; (b) Green preferences have flowed back to Labor at higher than typical rates. Melbourne Ports and Richmond are also “off-trend” but in a different class: the Labor vote there is in the low 30s (close to Labor’s national vote share), the Green vote at 17% (Richmond) or 19% (Melbourne Ports) – way above the Green’s national support level – helping put Labor over the top.

The AEC will eventually release preference flow data (here’s what that raw data looked like for 2010). Until then, some sense of the relationship between the Green vote and the impact on the election outcomes comes via the graph presented below. I’ve plotted the difference between ALP TPP and ALP 1st preferences against Green 1st preferences; again, the diagonal is a 45 degree line and the darker line is a smoothing spline.

Most of the data lies above the 45 degree line. That is, Labor accrues the vast majority of Green preferences and, of course, picks up preferences from other candidates too. Consequently, almost everywhere ALPTPP > ALP + Green. The exceptions are Bradfield, Curtin, Goldstein, Higgins, Kooyong, Mackellar, North Sydney, Warringah and Wentworth, all urban seats won by the Liberal Party. The Green vote in these seats is not small, and a reasonable proprtion of Green preferences flow back to the Coalition. A popular (if politically incorrect and not altogether accurate) euphemism for the Green > … > Liberal > … > ALP preference ordering is “doctor’s wives”. Imagining “leafy lined avenues” might help us get at the same niche of the electorate, without the patronizing, sexist overtones.

Note also the distinction between the Labor-won seats of Fowler, Blaxland and McMahon, versus, say, Grayndler, Melbourne Ports, Gellibrand and Sydney.

Perhaps all this is to say that not all Labor-won seats are the same, even those with reasonably similar outcomes on ALP TPP. The Green vote (and Green preference flow) is an interesting way to think about how those seats differ, but would themselves be explained by other things: e.g., level of tertiary education, income, espresso consumption, etc…

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