Galaxy 50-50; ReachTEL 51-49

Two recent polls:

• ReachTEL poll on 23 June came in at 51-49 in the Coalition's favour. This time the self allocated preferences largely reflect the flow of preferences at the last election. 
• Galaxy poll came in at 50-50

 Across the four models I run, here are the outcomes ... First the two-party preferred (TPP) model that assumes the house biases across pollsters cancel each other out.

The second model, also a TPP model, is anchored to the 2013 election outcome.

The third model is based on primary votes, anchored to the 2013 election outcome.

The final model is also based on primary votes. Like the first model above, it assumes that the house effects of pollsters cancel each other out (ie. they sum to zero).

Collectively, these models follow.

Galaxy 50-50

A Galaxy poll is out this morning with the headline result 50-50. The aggregation is unchanged, with the Coalition on 49.9 per cent.

This aggregation assumes that the tendencies of pollsters to lean one way or the other collectively cancel out, that is to say they sum to zero. A more detailed explanation of the data aggregation process can be found on this page.

Update

This morning the Murdoch tabloids have a new poll from Galaxy (the first since the Budget) at 51-49 in the Coalition's favour. This is a three point movement in the Coalition's favour since the previous Galaxy poll. The impact of this second poll on the post-Abbott aggregation is minimal: 50.2 to 49.8 per cent in the Coalition's favour.

The betting market appears to have settled.

	House	Coalition Odds ($)	Labor Odds ($)	Coalition Win Probability (%)
2015-09-18	Betfair	1.35	3.14	69.933185
2015-09-18	CrownBet	1.40	2.75	66.265060
2015-09-18	Ladbrokes	1.40	2.80	66.666667
2015-09-18	Luxbet	1.40	2.85	67.058824
2015-09-18	Sportsbet	1.40	3.00	68.181818
2015-09-18	TABtouch	1.26	3.75	74.850299
2015-09-18	William Hill	1.27	3.75	74.701195

First batch of post budget polling

It is the weekend after the Federal Budget and the blizzard of post Budget polling has started. There is a venerable tradition in Australian politics of wall-to-wall polling in the week that follows the Budget.

Mark Graph's first law of polling analysis is that most Budgets are meaningless events in the lives of most punters. Budgets have minimal (if any) impact on week-to-week movements in the national voting intention (particularly at the time of the Budget). Where they do have impact, measures that hurt are more likely to have an impact than measures that help. Furthermore, if a Budget measure does have an impact on voting intention, that impact is typically manifest closer to the time of implementation (when it actually hurts) than at the time of announcement.

Mark's second law: breathless reporting, where every micro-movement in the polls is over analysed, follows the Budget polling. In the melee, noise and signal become confused: one media outlet will proclaim the resurrection of the government and another will declare its Armageddon - all in the same week. The reporting of opinion polls in the week following the Budget is often little more than an exercise in intellectual masturbation for the titillation of those living inside the beltway.

Now that I have got that off my chest, let's look at the polls:

• ReachTEL has the national two-party preferred voting intention at 47-53 in Labor's favour. This is a movement of one percentage point in the government's favour since 23 April.
• Galaxy has the national two-party preferred voting intention at 48-52 in Labor's favour. This is a five percentage movement in the government's favour since February 2015.

Before moving to the charts, I need to acknowledge a few things. I have added some early 2014 data that I had missed, including the ACNielsen polling data before it ceased political polling. Because I use a sum-to-zero constraint in my model, these charts are not directly comparable with the earlier charts as a result.

In short, the government's fortunes continue to improve, but at a very slow pace. The government is still some distance from looking competitive were an election called at this time. All-in-all, there is not much to see in the post-Budget opinion polling.

Update

I shifted the graph production process from ggplot in R to matplotlib in python. Of necessity, this saw some analytical tasks move from R to python. In the process, it became clear that the LOWESS (localised regression) package in python statsmodels was not as robust as the conceptually similar LOESS package under R. For comparison, the first two of the remaining charts were produced in R. The subsequent charts were produced in python. I still run the Bayesian model in R/JAGS. However, I now export the model output data to python for chart production.

Correction

On the annotated charts, the last result was rounded to zero decimal places. This has been corrected to round to one decimal place.

Galaxy 43-57

Another published poll ahead of (now) Monday's spill motion. Today's Galaxy poll is no change on last week's poll: 43 to the Coalition, 57 to Labor.

I have made a pre-processing change to the Bayesian model. Before I explain that change, let me provide some context. Rather than resurrect my code base from the 2013 Election (I have about 40 or 50 model and processing files in that directory), I decided to code for the 2016 Election from scratch. Which is what I have done.

I had been thinking about the model output, and in particular how choppy that output appeared. To address the choppiness, I added a Henderson moving average. It worked. But it was not the most comfortable solution.

Last night, I noticed that in the lead-up to the 2013 Election, I reduced the sample size for the Morgan polls down to 1000 as an adjustment for the observed over dispersion given the sample size of the Morgan multi-mode polls. I have made this same adjustment for the 2016 models. It has had the effect of reducing the choppiness in the model. But it also means the outlier poll from the middle of 2014 no longer has such influence on the model. Consequently, the middle of 2014 is no longer the Bayesian nadir for the Coalition.

With today's Galaxy poll factored into the mix, the Bayesian model is now reporting the national voting intention at 44.6 to the Coalition, and 55.4 to Labor. This is pretty much the same result as Kevin Bonham, who puts it at 44.4 to 55.6.

Because I have made a change to the model, I will provide a fairly comprehensive set of charts.

Friday morning update

Two new polls at 47-53: Galaxy and ReachTEL.

Sunday update

Since the midweek update:

• Today's Murdoch press has an undated Galaxy poll (with an unreported sample size) - 47-53 in the Coalition's favour - a percentage point movement to the Coalition
• A ReachTEL poll with a status quo result - 47-53 in the Coalition's favour
• The latest Morgan poll (with preferences allocated using 2010 preference flows) - 46-54 in the Coalition's point - a 1.5 percentage point move to the Coalition

Dropping all of this into our Bayesian model yields the following:

At this point in the blog, it is my normal practice to remind people that I anchor the above Bayesian aggregation with the assumption that the net bias across all of the polling houses sums to zero. You will need to come to your own view about where the actual level of collective systemic bias lies for all the pollsters. At the 2010 Election (with a different set of pollsters), the population voting intention was about one percentage point more in the Coalition's favour compared with the pollster average (see here). In light of the 2010 experience, it is arguably plausible to subtract (say) half a percentage point or more from the above aggregation to adjust for the collective systemic bias across all of the polling houses. [As an aside, you will note that Simon Jackman, who seeks to anchor his Bayesian models with respect to the outcome of past elections regularly produces an aggregated poll that tracks well below the vast majority of individual poll results].