Saturday, June 30, 2018

Betting Market Update

This morning's quick look at betting markets sees some movement at Sportsbet.

House Coalition Odds ($) Labor Odds ($) Coalition Win Probability (%)
2018-06-30 CrownBet 2.25 1.47 39.52
2018-06-30 Ladbrokes 2.50 1.40 35.90
2018-06-30 Sportsbet 2.10 1.45 40.85
2018-06-30 William Hill 2.55 1.50 37.04

Sunday, June 24, 2018

Poll aggregation update

There were two new polls published last week, from Newspoll and Essential, both of which estimated the Coalition has 48 and Labor has 52 per cent of the two-party preferred (TPP) vote share. The aggregation of all polls has the Coalition on 47.9 and Labor on 52.1.

Cross checking this result against some simple moving averages, constrained such that house effects sum to zero, yields the following. Most of these moving averages are still factoring in the up-swing since November last year. I have mentioned before that these moving averages are less reliable around the endpoints than the Bayesian model.

My suspicion is that the Coalition's up-swing since late last year has run its course and we have seen fairly stable numbers for a month and a half or so now at around 48 per cent TPP for the Coalition. 

Turning to the primary vote estimates we have ...

In separate analysis, we can look at the Pauline Hanson One Nation Party results, which are included in the Other Parties primary vote chart immediately above ...

The TPP estimate from the logit primary vote model is less favourable to the Coalition than the published polls, using the preference flows from the most recent elections.

Saturday, June 23, 2018

The dramas of a daily web scraper

I have a set of web scraping programs I run every day to update the data for my election betting market series.

These programs are very short, typically 20 to 30 lines of Python code. But they are highly idiosyncratic. They break when a bookmaker updates the way in which it serves up web pages. My usual approach when this happens is to do a quick fix as soon as I see one of my scrapers has failed.

Sometime between Tuesday morning and Wednesday morning this week, Sportsbet updated the way in which it serves up web pages. It was a dramatic change. Sportsbet want from using bog standard HTML to a JavaScript page that dynamically creates the HTML on the fly.

This necessitated a different approach to web scraping. And I only found the time today (Saturday afternoon) to update the Sportsbet web scraper.

In the mean time, it looks like the odds have moved at Sportsbet.

Sportsbet now has the Coalition in the best position it has been in since I started my daily monitoring of odds for the winner of the next Australian federal election. In case you are wondering, the next federal election is most likely to be held in the first half of 2019, but it could happen earlier.

Sunday, June 10, 2018

Poll update

The latest aggregation follows. It treats the Newspolls since December 2017 as a different series to the earlier Newspolls. I have split Newspoll into two series on the basis of its treatment of One Nation preferences. The current two-party preferred (TPP) estimate, based on the assumption that house effects balance out on average, sees the Coalition on 47.8 per cent to Labor's election winning position of 52.2 per cent.

As a cross check, let's look at how this compares with a number of moving averages, which have been similarly adjusted on the assumption that house effects balance out on average. Both the LOWESS-91 and and Bayesian hierarchical model (above) suggest that the Coalition's poll position may have peaked and is now trending down.The moving averages are slower than the Bayesian to respond to changes in public opinion. They can also exaggerate the end point position.

We can also compare the estimated house biases from the various moving averages compared with the Bayesian model above.

Essential Ipsos Newspoll Newspoll2 ReachTEL Roy Morgan YouGov Iter Sum Errors Squared
HMA-181 -0.805492 -0.864758 -0.792727 0.073339 -0.324017 0.511941 2.201714 22 0.008374
HMA-365 -0.781727 -0.742800 -0.723322 0.054020 -0.300477 0.293336 2.200970 20 0.009416
LOWESS-91 -0.801099 -0.883610 -0.807314 0.132668 -0.290249 0.443300 2.206304 19 0.008246
LOWESS-181 -0.803521 -0.804463 -0.770847 0.111452 -0.311898 0.369247 2.210029 16 0.009263

Let's move to the TPP analysis based on primary votes and preference flows at the last Federal election. This use of preference flows is less favourable to the Coalition than the latest flows at Newspoll. We are not seeing a downturn in any of these series. This might be the additional constraints in the primary vote model makes it less responsive to chnages in public sentiment. But this might be because the model does not take account of One Nation preference flows separately from other parties in the others category.

The primary vote share estimates follow.

Separating One Nation from Other above ... we can see a party that appears to be in decline, and well down on its peak in early 2017.