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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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where will the two-party preferred result land?

Monday September 23, 2013

Filed under: Australian Politics — jackman @ 7:06 pm

We’re still waiting for TPP counts in 10 “non-classic” seats. With the TPP counting basically done in the other 140 seats, Labor has 46.61% TPP.

We’ll know soon enough, but my very rough guess goes something like this:
Screen Shot 2013-09-23 at 7.02.12 PM

That is, Labor picks up TPP swings against it in the 10 non-classic divisions awaiting TPP counts. I weight my rough guesses in these seats by each seat’s enrollment, getting 42.92% ALP TPP there. These 10 seats have total enrollment of 933K, which goes up against the 46.61% from the 14.7M – 933K of the electorate in the 140 seats with a TPP count. Overall result: about 46.4%.

But this estimate is as rough as guts, as they say… All the same, this would put the 2013 result in 1996 territory, where Labor got 46.37% TPP.

Update: another approach to the data generates a similar estimate. The 10 non-classic seats in 2013 produced 46.84% ALP TPP in 2010. The remaining 140 classic seats gave us 50.34%, the difference being 3.5 percentage points. The weighted combination of the 10 “non-classic” plus 140 “classic” divisions in 2010 is 50.12%, the overall 2010 ALP TPP result.

If we get that 3.5 percentage point classic/non-classic difference this year, then the 10 non-classic divisions will come in at 46.61-3.5 = 43.11% ALP TPP. This implies an overall ALP TPP result of 46.39%, again in 1996 territory.

We’d need the 10 non-classic divisions to produce something like 40.5% ALP TPP for the overall ALP TPP result to get down to 46.2% (the last point estimate I produced from my poll averaging machinery ahead of the election). We still might get there, but these rough estimates as to ALP TPP among the non-classic divisions suggests 46.3-46.5 might be more like it.

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collection of my 2013 election analyses, lots of graphs and more to come

Friday September 20, 2013

Filed under: Australian Politics — jackman @ 12:08 am

I’ve created a page holding links to the various graphs and analyses I’ve got out of the 2013 Australian election.

This is still a work in progress. I’m sitting on quite a lot more content to go up yet. A sampler, for your consideration: two-party preferred swings, grouped by state… (click for a hi-res PDF in a separate window):

Two-party preferred swings, by electoral division, 2013 Australian Federal election, grouped by state

Moreover, the vote count continues, and will for a while. Many of the graphs I’m making update as the vote count continues; I’ve got time and date stamps on most of the output that is still in flux. The two-party preferred count will bounce around a bit once the AEC performs what is known as a “scrutiny for information” in 10 “non-classic” seats that aren’t ALP-Coalition two-party contests.

The vote count has settled down enough for another look at the performance of the marginal seat polls and the betting markets. At the seat-by-seat level, neither particular can claim a ton of glory.

I took a quick look at the marginal seat polling in a column I bashed out for Guardian Australia very late on Election Night; that needs to be updated and looked at a bit more carefully. I tend to think that the small samples used in much of that seat-specific polling will actually work to the pollsters’ advantage in this case; with so much sampling error in the estimates, the misses recorded by those polls will have to extremely large for us to be able to confidently conclude they are biased, or to say that one pollster is more biased than another.

But we’ll see. Its great when there is a data analysis ahead of you where you really don’t know how it will turn out.

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final run of the 2013 poll averaging model: Labor 46.2% TPP

Friday September 6, 2013

Filed under: Australian Politics,statistics — jackman @ 2:18 pm

I’m looking to see if I have missed something, but I think thats it. I’ve got the releases yesterday, including the 54-46 results from Newspoll and Nielsen:

Screen Shot 2013-09-06 at 2.53.45 PM

Entering all this into the poll averaging model produces an ALP TPP estimate of 46.2%, +/-0.9. The 90-day trajectory (click for larger view):

modelAverage20130907-90
This estimate is formed as a 67/33 combination of

  1. the model that is constrained to fit the 2010 election result exactly, and produces a set of house effects that are all positive (i.e., virtually all pollsters overestimated Labor’s 2010 TPP performance), which produces an estimate of 45.7% ALP TPP
  2. a model that is identified by assuming the house effects sum to zero (i.e., the polling industry is collective unbiased); this model produces an estimate of 47.1%.

I’ve left out the Lonergan mobile-only poll with n < 900; given that it was mobile-only, robo, I would have entered it into the model with its own unknown house effect. A pollster with an unknown house effect sees the impact of their estimate be greatly diminished, since the uncertainty generated by not knowing their house effect (and having only one poll with which to estimate it) winds up dramatically downweighting the effect of the poll on the overall estimate. Since this was a poll with a reasonably small sample size, it would have had a very small impact on the results in any event. I'll go ahead and re-run the models now with it in, but it won't change much at all, I should think.

Morgan multi-mode at 46.5 is interesting. Morgan multi-mode was showing a house effect of ALP +2, but then the last poll comes in very very close to the model consensus, dragging down the model consensus (even with some discount terms in the model) a little. There'll be time for "drop one pollster at a time" sensitivity analyses after the election, etc.

Screen Shot 2013-09-06 at 3.03.20 PM

Update (7.38am AEST): it turns out that Morgan’s final numbers differed slightly from those I had in the analysis, same TPP estimate, just bigger stated sample size and the field period closed Sept 6. Re-running…

Update (10.31am AEST): No change. Lonergan and fixed Morgan field period and sample size leave model estimate at 46.2% ALP TPP. See the graph above.

Comments (17)

Morgan phone 57-43, model-based poll average moves to 47.3% Labor TPP

Wednesday August 14, 2013

Filed under: Australian Politics — jackman @ 10:22 pm

A phone poll by Morgan on August 12 and 13 resulted in 57% TPP for the Coalition, 52% Coalition primary vote, ALP 31%, Greens 9%. n=569.

“Yeah, right.”

And Morgan themselves are pouring cold water on the result:

Gary Morgan says:

“It needs to be remembered that telephone polls are biased towards the party that receives the best publicity. Tony Abbott’s ‘free kick’ from News Corp over the last few days accusing Rudd of cheating in the debate by using notes has no doubt boosted the Opposition Leader’s credibility although his comment yesterday on ‘sex appeal’ was crass, definitely irrelevant and unnecessary. Prediction: You can expect all telephone polls conducted over the next few days to show a jump in support for the Liberal-National Party!”

Maybe, but 57-43?

And the only problem with Morgan trying to downplay this result is that Morgan’s last phone poll before the 2010 election actually did pretty well: a small over-estimate of the Labor primary vote (39 vs 38) and 51% for the Labor TPP (actual was 50.12%). See my GA post on this from yesterday.

In fact, Morgan phone polls have the best track record of the various interview modes they use, based on my recollection of the various analyses I’ve done on this over the years. My model assigns a pretty small house effect to Morgan phone polls (+0.6pp for Labor TPP, +/- 0.5pp). Compare Morgan’s other poll modes: face-to-face, +2.4pp Labor TPP, +/- 0.5pp; multi-mode, +2.1 Labor TPP, +/- 0.5pp.

Prior to this Morgan phone poll coming in the model was putting Labor in the high 47s. Even with the small nominal n of this poll (569), the Bayesian compromise has to move in the direction of the new data point (43%, modulo the small house effect estimate). Accordingly, my calculations suggest that the new estimate is 47.3% Labor TPP +/- 1.5pp.

New numbers and graphs will appear at the links etc in the header of my blog in the next few hours.

This poll is one of the “worst-fitting” data points I’ve got in the data set of 261 polls I’m currently working with, 2010-present. That is, given all the other polling, given the estimate of the (small) Morgan phone house effect, something like 48% Labor TPP would have been more like it, +/- 4.6pp, given the small nominal sample size. 43% Labor TPP under these circumstances is, well, an unusual result given what else we’re observing, and all that we’ve observed about the performance of Morgan phone polls in the past.

This influence of this data point will get steam-rollered by the next round of polling, but for now, there it is…

Comments (3)

cricket and politics

Monday August 12, 2013

Filed under: Australian Politics,general — jackman @ 11:09 am

Utterly unscientific, but I can’t help but think the incumbent (Labor) would be doing better if Australia had a better cricket side right now.

Screen Shot 2013-08-12 at 11.08.41 AM

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Nielsen 52-48 moves poll average to 48.1% ALP 2PP, Centrebet follows

Friday August 9, 2013

Filed under: Australian Politics — jackman @ 6:47 pm

Nielsen’s 52-48 (n=1400) poll (png from GhostWhoVotes) bumped my Guardian Australia poll average a little, Labor moving from 48.2% TPP to 48.1% TPP, a new post-Rudd-return low.

Centrebet’s prices have moved this morning, Labor now out to 4.90 5.50, the Coalition in to 1.18 1.15, for an implied probability of a Labor win of less than 20% (19.4% 17.3%). Galaxy must be due to drop some numbers soon, perhaps in the Sunday News tabloids. We’ll also have Morgan’s mega-multi-mode melange and Essential’s two-week rolling average released early next week. The leader’s debate might also bring out some other polling.

I’m also publishing the GA poll average here on my own blog: see the growing list of Australian election stats and links appearing in the header of my blog, above.

The model-based average gets updated as we enter new polls into the database, along with a graph showing the trajectory of the model’s estimate of ALP 2PP voting intentions over the last 90 days:

Comments (13)

Forde flips on back of Beattie bid news

Wednesday August 7, 2013

Filed under: Australian Politics — jackman @ 5:21 pm

Labor’s price has come in from 1.75 (sportsbet) and 2.05 (Centrebet) to 1.20 and 1.25 respectively.

The implied probability of a Labor win in Forde is 68% and 71%, up from 47% and 42%. Meh.

Labor expected seat count: 61.

Forde’s really changed its status in my probability by margin plot.

Three probable Labor pickups in the top left quadrant of the graph: Forde, Melbourne (from the Greens), Brisbane.

The betting markets still tip 11 probable Labor loses, lower right quadrant.

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Labor close to post-Rudd lows at Centrebet

Tuesday August 6, 2013

Filed under: Australian Politics — jackman @ 6:20 pm

Labor’s out to 4.50 4.80 at Centrebet, the Coalition in to 1.20 1.18, for an implied ALP win probability of 21% 19.7%.

That just about takes us back to June 27, when Labor’s price came back in from beyond $5.00 on the back of Rudd’s return to the leadership.

Just one week ago (noon July 31) Labor was at 33% (2.90 to 1.40).

Labor’s post-Rudd peak at Centrebet was around 35% on July 16 (2.70 to 1.45).

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Newspoll the market mover (redux redux redux)

Monday July 22, 2013

Filed under: Australian Politics — jackman @ 10:22 am

52-48 TPP to the Coalition overnight from Newspoll (The Australian).

The betting markets haven’t wasted anytime responding. Indeed, Labor’s price could ease further through the day as news of the poll (and spin re poll) circulates.

As a result, the 1st digit is a “2”, not a “3”, on the probability of a Labor win, implied by the prices; see the graphs (links at the header of the blog), at least for now. Thats still a long way up from pre-Rudd levels, but a long way short of 50% or better.

Implied ALP win probability over the last week, at the 3 bookies I’m following closely (click for larger view):

Screen Shot 2013-07-22 at 10.18.36 AM

Newspoll’s influence on Australian political discourse and indicators like the betting markets is really something to behold. I’ve blogged on it numerous time over the years here (e.g., Nov 2011; May 2010; Nov 2007; Sept 2007). This topic is something I’ll try to expand on my piece this week for the Guardian Australia.

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