Saturday, August 17, 2013

What are the punters thinking?

This morning my wife asked me why have I not blogged for a while. The short answer is that I am a little bored with the election campaign. There has not been much in the way of national opinion polls over the past week. While there has been a number of individual seat polls, these were all consistent with a sizable Coalition victory come September 7. Put simply, there was not much new to report.

To cure my boredom, I have been looking at the Centrebet individual seat odds. I have jerry-built a web-scraper and converted the results to the following table (the run was at 6.45pm on Saturday 17 August). Each row in the table represents a seat. The first column is the seat name. The second column is the state. The next three columns are the probabilities of a Labor, Coalition or Other win, expressed as a percentage (calculated from the odds and adjusted for the bookmaker's over-round). The "current" column indicates the party that currently holds the seat. The "favourite" column indicates the party the bookmaker's favour to win the seat. The final column is whether this would represent a change to the composition of the parliament at the time of its dissolution (Labor: 71; Coalition: 72; Others: 7). The table is ordered from the least probable result to the most probable result. Below the table are some observations.


State Labor Coalition Other current favourite change
Moreton QLD 45.7 49.5 4.8 Labor Coalition TRUE
Eden-Monaro NSW 50.4 44.1 5.4 Labor Labor FALSE
Lingiari NT 52.3 40.2 7.5 Labor Labor FALSE
Lilley QLD 54.5 41.8 3.8 Labor Labor FALSE
Petrie QLD 54.8 42.1 3.1 Labor Labor FALSE
Banks NSW 39.9 54.9 5.2 Labor Coalition TRUE
Parramatta NSW 55.5 37.4 7.1 Labor Labor FALSE
Brisbane QLD 38.4 56.9 4.7 Coalition Coalition FALSE
Brand WA 58.4 35.7 5.9 Labor Labor FALSE
Capricornia QLD 58.5 35.8 5.8 Labor Labor FALSE
Lyons TAS 58.6 35.9 5.5 Labor Labor FALSE
Page NSW 58.8 36.0 5.1 Labor Labor FALSE
Blair QLD 60.0 36.7 3.3 Labor Labor FALSE
Reid NSW 35.1 60.6 4.3 Labor Coalition TRUE
Robertson NSW 30.4 60.8 8.8 Labor Coalition TRUE
Kingsford Smith NSW 61.0 34.7 4.3 Labor Labor FALSE
Solomon NT 32.4 62.5 5.1 Coalition Coalition FALSE
La Trobe VIC 31.9 62.6 5.5 Labor Coalition TRUE
Dobell NSW 29.5 63.3 7.2 Other Coalition TRUE
Barton NSW 63.7 29.7 6.6 Labor Labor FALSE
Greenway NSW 32.8 64.4 2.9 Labor Coalition TRUE
McEwen VIC 65.3 30.4 4.3 Labor Labor FALSE
Hindmarsh SA 65.6 30.5 3.9 Labor Labor FALSE
Franklin TAS 66.3 26.9 6.8 Labor Labor FALSE
Forde QLD 28.4 66.6 5.0 Coalition Coalition FALSE
Richmond NSW 67.0 26.0 7.1 Labor Labor FALSE
Longman QLD 27.5 67.6 5.0 Coalition Coalition FALSE
Braddon TAS 27.5 67.8 4.7 Labor Coalition TRUE
Bonner QLD 27.6 68.0 4.3 Coalition Coalition FALSE
Melbourne VIC 68.3 2.6 29.1 Other Labor TRUE
Dawson QLD 25.7 68.4 5.9 Coalition Coalition FALSE
Hasluck WA 27.9 68.8 3.3 Coalition Coalition FALSE
Herbert QLD 25.9 68.8 5.3 Coalition Coalition FALSE
Flynn QLD 24.8 68.9 6.3 Coalition Coalition FALSE
Chisholm VIC 69.4 24.8 5.8 Labor Labor FALSE
Werriwa NSW 70.8 25.3 3.9 Labor Labor FALSE
Adelaide SA 70.9 23.1 6.0 Labor Labor FALSE
Swan WA 23.8 72.3 4.0 Coalition Coalition FALSE
Deakin VIC 20.2 72.7 7.1 Labor Coalition TRUE
McMahon NSW 73.4 23.6 3.1 Labor Labor FALSE
Bass TAS 20.5 74.0 5.5 Labor Coalition TRUE
Casey VIC 18.1 74.8 7.1 Coalition Coalition FALSE
Lindsay NSW 20.9 75.2 3.9 Labor Coalition TRUE
Newcastle NSW 75.3 16.1 8.7 Labor Labor FALSE
Bruce VIC 75.6 18.1 6.3 Labor Labor FALSE
Denison TAS 19.5 4.9 75.6 Other Other FALSE
Leichhardt QLD 18.1 75.6 6.3 Coalition Coalition FALSE
Boothby SA 18.3 75.8 5.9 Coalition Coalition FALSE
Aston VIC 18.2 75.9 5.9 Coalition Coalition FALSE
Canning WA 19.6 76.1 4.3 Coalition Coalition FALSE
Corangamite VIC 16.3 76.3 7.4 Labor Coalition TRUE
Dunkley VIC 16.3 76.6 7.0 Coalition Coalition FALSE
Melbourne Ports VIC 76.9 16.4 6.8 Labor Labor FALSE
Fairfax QLD 6.6 77.1 16.2 Coalition Coalition FALSE
Fremantle WA 77.6 16.6 5.8 Labor Labor FALSE
Gilmore NSW 16.6 77.9 5.5 Coalition Coalition FALSE
Macquarie NSW 16.7 78.2 5.1 Coalition Coalition FALSE
Bendigo VIC 78.4 15.0 6.6 Labor Labor FALSE
Indi VIC 4.0 78.7 17.2 Coalition Coalition FALSE
Throsby NSW 78.9 14.4 6.7 Labor Labor FALSE
Rankin QLD 78.9 18.0 3.1 Labor Labor FALSE
Fisher QLD 12.2 79.0 8.8 Other Coalition TRUE
Hinkler QLD 10.5 79.2 10.3 Coalition Coalition FALSE
Fowler NSW 79.4 16.9 3.7 Labor Labor FALSE
McMillan VIC 14.6 79.4 6.0 Coalition Coalition FALSE
Chifley NSW 79.9 14.6 5.5 Labor Labor FALSE
Perth WA 80.0 13.3 6.7 Labor Labor FALSE
Wakefield SA 80.7 13.4 5.9 Labor Labor FALSE
Macarthur NSW 14.8 80.8 4.4 Coalition Coalition FALSE
Fadden QLD 10.0 81.4 8.7 Coalition Coalition FALSE
Bowman QLD 13.5 81.4 5.1 Coalition Coalition FALSE
Wright QLD 5.8 81.6 12.6 Coalition Coalition FALSE
Oxley QLD 81.7 15.0 3.3 Labor Labor FALSE
Ryan QLD 10.1 82.2 7.8 Coalition Coalition FALSE
Bennelong NSW 13.7 82.4 3.9 Coalition Coalition FALSE
Stirling WA 10.8 82.5 6.7 Coalition Coalition FALSE
Jagajaga VIC 82.6 11.6 5.8 Labor Labor FALSE
Watson NSW 83.0 12.7 4.4 Labor Labor FALSE
Charlton NSW 83.3 11.7 5.1 Labor Labor FALSE
Isaacs VIC 83.3 11.7 5.1 Labor Labor FALSE
Ballarat VIC 83.9 10.3 5.9 Labor Labor FALSE
Cowan WA 10.3 83.9 5.9 Coalition Coalition FALSE
Hunter NSW 83.9 10.9 5.1 Labor Labor FALSE
Batman VIC 83.9 5.7 10.4 Labor Labor FALSE
Makin SA 84.2 11.9 4.0 Labor Labor FALSE
Sydney NSW 84.3 5.7 10.1 Labor Labor FALSE
Hughes NSW 11.1 84.6 4.4 Coalition Coalition FALSE
Blaxland NSW 84.9 11.1 3.9 Labor Labor FALSE
Griffith QLD 85.0 9.6 5.4 Labor Labor FALSE
Dickson QLD 9.8 85.0 5.1 Coalition Coalition FALSE
Shortland NSW 85.2 9.7 5.1 Labor Labor FALSE
Canberra ACT 85.3 8.8 5.9 Labor Labor FALSE
Cunningham NSW 85.4 8.7 5.9 Labor Labor FALSE
Kooyong VIC 6.6 85.5 7.9 Coalition Coalition FALSE
Kingston SA 85.5 9.8 4.7 Labor Labor FALSE
Lalor VIC 85.7 7.2 7.1 Labor Labor FALSE
Kennedy QLD 5.0 9.4 85.7 Other Other FALSE
Berowra NSW 6.7 85.8 7.5 Coalition Coalition FALSE
Lyne NSW 8.8 86.1 5.2 Other Coalition TRUE
Hume NSW 7.3 86.3 6.4 Coalition Coalition FALSE
Corio VIC 86.4 7.3 6.4 Labor Labor FALSE
Flinders VIC 6.7 86.5 6.8 Coalition Coalition FALSE
Cook NSW 6.7 86.5 6.8 Coalition Coalition FALSE
Wentworth NSW 5.1 86.7 8.2 Coalition Coalition FALSE
Maribyrnong VIC 86.8 7.3 5.9 Labor Labor FALSE
Sturt SA 8.0 86.8 5.1 Coalition Coalition FALSE
Higgins VIC 6.7 86.8 6.4 Coalition Coalition FALSE
Paterson NSW 8.0 86.9 5.1 Coalition Coalition FALSE
McPherson QLD 6.8 86.9 6.3 Coalition Coalition FALSE
Grey SA 6.8 87.0 6.3 Coalition Coalition FALSE
Gippsland VIC 6.8 87.0 6.2 Coalition Coalition FALSE
Barker SA 6.8 87.1 6.2 Coalition Coalition FALSE
Calare NSW 7.3 87.1 5.6 Coalition Coalition FALSE
Curtin WA 4.2 87.2 8.6 Coalition Coalition FALSE
Bradfield NSW 5.9 87.2 6.9 Coalition Coalition FALSE
Grayndler NSW 87.2 5.2 7.6 Labor Labor FALSE
Mackellar NSW 5.2 87.2 7.6 Coalition Coalition FALSE
North Sydney NSW 5.9 87.2 6.9 Coalition Coalition FALSE
Goldstein VIC 6.8 87.3 5.9 Coalition Coalition FALSE
Scullin VIC 87.3 6.8 5.9 Labor Labor FALSE
Moore WA 6.8 87.3 5.9 Coalition Coalition FALSE
Holt VIC 87.5 7.4 5.1 Labor Labor FALSE
Hotham VIC 87.5 7.4 5.1 Labor Labor FALSE
Parkes NSW 8.1 87.5 4.4 Coalition Coalition FALSE
Forrest WA 6.6 87.7 5.7 Coalition Coalition FALSE
Wide Bay QLD 5.9 87.7 6.4 Coalition Coalition FALSE
Mallee VIC 6.8 87.7 5.4 Coalition Coalition FALSE
Warringah NSW 5.2 87.8 7.0 Coalition Coalition FALSE
Moncrieff QLD 6.9 87.9 5.2 Coalition Coalition FALSE
Calwell VIC 88.0 6.8 5.2 Labor Labor FALSE
Gorton VIC 88.0 6.8 5.2 Labor Labor FALSE
Fraser ACT 88.1 5.9 6.0 Labor Labor FALSE
New England NSW 6.8 88.1 5.0 Other Coalition TRUE
Murray VIC 6.8 88.1 5.0 Coalition Coalition FALSE
Gellibrand VIC 88.3 5.2 6.4 Labor Labor FALSE
Menzies VIC 5.3 88.4 6.4 Coalition Coalition FALSE
Cowper NSW 7.5 88.6 3.9 Coalition Coalition FALSE
Mayo SA 5.3 88.7 6.0 Coalition Coalition FALSE
Mitchell NSW 6.9 88.7 4.4 Coalition Coalition FALSE
Tangney WA 6.0 88.8 5.2 Coalition Coalition FALSE
Port Adelaide SA 89.1 6.0 4.9 Labor Labor FALSE
Riverina NSW 6.9 89.1 4.0 Coalition Coalition FALSE
Pearce WA 5.2 89.2 5.6 Coalition Coalition FALSE
Maranoa QLD 5.3 89.4 5.2 Coalition Coalition FALSE
Farrer NSW 6.0 89.5 4.4 Coalition Coalition FALSE
Wills VIC 89.9 3.5 6.6 Labor Labor FALSE
Groom QLD 6.1 90.5 3.4 Coalition Coalition FALSE
Wannon VIC 4.4 91.5 4.1 Coalition Coalition FALSE
O'Connor WA 3.3 93.0 3.7 Coalition Coalition FALSE
Durack WA 3.3 93.9 2.8 Coalition Coalition FALSE

The first thing to observe is that the Coalition is the favourite in 87 seats; Labor in 61 and Others (Bob Katter and Andrew Wilkie) in two seats. If the favourite got up in every seat, it would be a pretty convincing win for the Coalition.


Coalition Labor Other
Seat count: 87 61 2

The Cube Law asserts that the ratio of seats a party wins at an election is approximately a cube of the ratio of votes the party won in that election. We can express this algebraically as follows (where s is the proportion of seats won by a party and v is the proportion of votes won by the party). Both s and v lie in the range from 0 to 1.
If we assume that Wilke breaks Labor and Katter breaks for the Coalition, we can apply the cube law to get an estimate of the TPP Labor vote implied by the punters. If we take the cube root of 62/88 we get 0.88982. Let's call this value k. We can then solve for v to show that the punters think the two-party preferred vote share will be: v = k / (k + 1). In this case, the punters are predicting a TPP vote share around 47.1 per cent for Labor.

In this context, let's look at the (so called) bellwether seats. Intriguingly, one of the historic bellwethers - Makin - is tipped to lose its bellwether status. The punters think it will stay with Labor. Other bellwether seats - Lindsay and Robinson - are tipped for a change at this election. On two bellwethers, the punters are undecided (itself an interesting fact). The odds in Moreton in Queensland and Eden-Monaro in NSW are pretty close to a line ball. In probability terms they are a coin-flip. Collectively the punters think they could go either way. While the punters think the over-all result is certain, they are hedging on these two bellwether seats.

The next thing to look at is the "others". As noted above, the punters think Andrew Wilkie and Bob Katter have a damned good chance of being returned. The punters  give Adam Bandt for the Greens less than a 30 per cent chance of being returned in the seat of Melbourne (paying $3.30 for the win). Clive Palmer's tilt in the seat of Fairfax has Centrebet paying $6.50 for "any other candidate". Similarly, Cathy McGowan's tilt in the seat of Indi has Centrebet paying $6.50 for an "Independent".

My final observation is with the captain's pick for Forde. The punters think that Bert van Manen will beat former premier, Peter Beattie.

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6 comments:

  1. UnknownAugust 17, 2013 at 8:08 PM

    Bandt is a good lay at 3.30. Closer to 6 in my mind. Otherwise good work on the scraper!

    ReplyDelete
  2. David BarryAugust 17, 2013 at 8:30 PM

    Makin's odds aren't too intriguing, since it's now on a 12% margin. Under Gillard, Labor seemed to be polling disastrously in South Australia, and according to the bookies they were only a 75% chance of holding Makin for a while. But it's back to being considered safe under Rudd.

    The odds in Forde changed drastically after the Lonergan and JWS polls showed Beattie trailing - the previous day the four-bookie average implied probability of a Labor win there was 61%. (The implied probabilities I've given assume that each seat is really a two-candidate contest; to make them comparable with your table you should probably knock 5 or 6 percentage points off them.)

    ReplyDelete
    Replies
    1. Mark GraphAugust 17, 2013 at 8:54 PM

      Also, agree that the betting odds today have been affected by raft of robo-call seat polls over the past couple of days (see Poll Bludger: http://blogs.crikey.com.au/pollbludger/2013/08/16/marginals-robo-poll-bonanza/). These have all implied a larger swing than the national polls have suggested. It will be interesting to see how the national polls out over the next couple of days tally with the the robo-call polls.

      Delete
  3. Mark GraphAugust 17, 2013 at 8:51 PM

    A pretty good achievement for a local member to take a marginal seat and make it safe in two terms (and one smallish redistribution).

    ReplyDelete
  4. Not TrampisAugust 18, 2013 at 9:01 AM

    got you in and splendid work as usual

    ReplyDelete
  5. Kevin BonhamAugust 18, 2013 at 4:53 PM

    I reckon the 47.1% 2PP implied by the cube rule is also very close to the result required for 87-61, if modelled off the pendulum with allowance made for normal variations from uniform swing. Under a uniform swing assumption a 2PP of between 46.4 and 46.8 loses 12 seats with the assumed gain of Melbourne. But Labor holds more seats that would be just above the line of a uniform swing of that level than that would be just below, so the 2PP to lose 12 seats should, all else being equal, be slightly higher than that range.

    The seat betting favourites as listed above for Queensland are the same as they were when seat odds were first returned after Rudd came back. The total number of seats is as it was in the second week of the Rudd return with very little change in individual seats (Moreton and Lingiari were at that stage the other way around.)

    Seat betting market favourite tallies have moved with the polls to some degree but on the whole have been very stable.

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