September 28, 2015

Rugby World Cup Predictions, 29 September 2015 to 03 October 2015

It is a little difficult to choose a period for the predictions. I have predicted up to October 3 because Tonga plays a further game on October 4, and I want to have updated their rating based on the result of the Tonga-Namibia game before predicting their game against Argentina.

Team Ratings at 29 September

The basic method is described on my Department home page.

Here are the team ratings prior to 29 September along with the ratings at the start of the Rugby World Cup.

	Rating at 29 September	Rating at RWC Start	Difference
New Zealand	27.38	29.01	-1.60
South Africa	21.98	22.73	-0.70
Australia	20.47	20.36	0.10
Ireland	17.72	17.48	0.20
England	17.29	18.51	-1.20
Wales	14.10	13.93	0.20
France	11.53	11.70	-0.20
Argentina	9.03	7.38	1.60
Scotland	6.00	4.84	1.20
Fiji	-3.23	-4.23	1.00
Samoa	-3.54	-2.28	-1.30
Italy	-6.93	-5.86	-1.10
Tonga	-7.23	-6.31	-0.90
Japan	-10.61	-11.18	0.60
USA	-15.69	-15.97	0.30
Georgia	-17.57	-17.48	-0.10
Canada	-18.06	-18.06	-0.00
Romania	-20.20	-21.20	1.00
Uruguay	-31.10	-31.04	-0.10
Namibia	-34.63	-35.62	1.00

Performance So Far

So far there have been 19 matches played, 16 of which were correctly predicted, a success rate of 84.2%.
Here are the predictions for previous games.

	Game	Date	Score	Prediction	Correct
1	England vs. Fiji	Sep 18	35 – 11	29.20	TRUE
2	Tonga vs. Georgia	Sep 19	10 – 17	11.20	FALSE
3	Ireland vs. Canada	Sep 19	50 – 7	35.50	TRUE
4	South Africa vs. Japan	Sep 19	32 – 34	33.90	FALSE
5	France vs. Italy	Sep 19	32 – 10	17.60	TRUE
6	Samoa vs. USA	Sep 20	25 – 16	13.70	TRUE
7	Wales vs. Uruguay	Sep 20	54 – 9	51.50	TRUE
8	New Zealand vs. Argentina	Sep 20	26 – 16	21.60	TRUE
9	Scotland vs. Japan	Sep 23	45 – 10	14.40	TRUE
10	Australia vs. Fiji	Sep 23	28 – 13	24.10	TRUE
11	France vs. Romania	Sep 23	38 – 11	33.30	TRUE
12	New Zealand vs. Namibia	Sep 24	58 – 14	64.00	TRUE
13	Argentina vs. Georgia	Sep 25	54 – 9	24.60	TRUE
14	Italy vs. Canada	Sep 26	23 – 18	12.50	TRUE
15	South Africa vs. Samoa	Sep 26	46 – 6	23.90	TRUE
16	England vs. Wales	Sep 26	25 – 28	11.20	FALSE
17	Australia vs. Uruguay	Sep 27	65 – 3	50.30	TRUE
18	Scotland vs. USA	Sep 27	39 – 16	21.40	TRUE
19	Ireland vs. Romania	Sep 27	44 – 10	38.80	TRUE

Predictions for 29 September to 03 October

The prediction is my estimated expected points difference with a positive margin being a win to the first-named team, and a negative margin a win to the second-named team.

	Game	Date	Winner	Prediction
1	Tonga vs. Namibia	Sep 29	Tonga	27.40
2	Wales vs. Fiji	Oct 01	Wales	23.80
3	France vs. Canada	Oct 01	France	29.60
4	New Zealand vs. Georgia	Oct 02	New Zealand	44.90
5	Samoa vs. Japan	Oct 03	Samoa	7.10
6	South Africa vs. Scotland	Oct 03	South Africa	16.00
7	England vs. Australia	Oct 03	England	3.30

David Scott obtained a BA and PhD from the Australian National University and then commenced his university teaching career at La Trobe University in 1972. He has taught at La Trobe University, the University of Sheffield, Bond University and Colorado State University, joining the University of Auckland, based at Tamaki Campus, in mid-1995. He has been Head of Department at La Trobe University, Acting Dean and Associate Dean (Academic) at Bond University, and Associate Director of the Centre for Quality Management and Data Analysis at Bond University with responsibility for Short Courses. He was Head of the Department of Statistics in 2000, and is a past President of the New Zealand Statistical Assocation. See all posts by David Scott »

Comments

Jaco Griesel

Hi there, prof Scott!

I stumbled upon your predictions for the RWC2015 Week 1, and has since been a true believer!

I would like to use your method in other rugby competitions, but the details you provide on your homepage lack some specifics – especially for somebody who had Stats 114 and Stats 144 at university 20 years ago… Is it possible you can explain your method in more detail, please?

Thanks in advance, and keep those predictions coming! I don’t know if you play SuperBru (www.superbru.com), but I definitely know you’ll kick serious butt if you do! (Since I’ve been using your predictions, I’ve gone from “Top 85%” to “Top 5%” on average in the groups I play in!)

Best regards,

Jaco
(Wellington, South Africa)

9 years ago
- David Scott
  
  I believe some of my other readers go in for SuperBru. There might be diminishing returns if more players use my predictions as a guide.
  
  As for the method, you need to bone up on exponential smoothing. But you start with all teams with equal rating some years before you want to make a prediction (hence you need a lot of past data). Then for each game you predict using ratings and a home ground advantage. After you get the result you update the ratings of each team by taking a fraction of the difference between your prediction and the actual (that difference is the error, hence error-correction exponential smoothing). Do that for many, many games, and for different values of the home ground advantage and the fraction used in the updating. Choose the best values of the home ground advantage and the fraction.
  
  There are some tweaks to that but that is all it is. There is art in choosing the parameters and some additional parameters involved in the tweaks that I just mentioned, and there is computing skill needed to do things efficiently so I can predict four different competitions at the moment without spending a lot of time on it.
  
  9 years ago
Steven Bott

David,

Unless I am mistaken, your success rate is not accurate.

For example;

France v Romania – prediction 33.3 – result 27

NZ v Namibia – prediction 64 – result 44

Arg v Georgia – prediction 24.6 – result 45

And the list goes on.

I may have misunderstood the prediction concept.

Please clarify.

Thanks

9 years ago
- Thomas Lumley
  
  I think you’ve misunderstood the summary of results: a prediction is counted as correct if the result is in the same direction as the prediction.
  
  9 years ago
- David Scott
  
  As Thomas said, the accuracy relates only to whether I predicted the winner correctly. Predicting margins, even within a few points would be ridiculously hard.
  
  9 years ago
- Jaco Griesel
  
  I agree with the two gentlemen. Also remember that there is absolutely no way you can account statistically for ever-changing team selections, injuries, one bad bounce of the ball, a bad decision by a captain (Eng vs Wales comes to mind!) and many other factors that can influence the outcome and/or scores.
  
  All three outcomes that were “wrong” up to this point were seen as massive upsets by the rugby world, and if you look at those games, the factors I mentioned above all played a role. Except with the SA v JAPAN game – those Springboks were just poor! And yeah, I’m a Bok supporter.
  
  9 years ago
  - Mark Dalton
    
    Jaco, I don’t agree that Wales over England was a massive upset. As a former UK resident and hence follower of the intense rivalry between those ‘home nation’ teams, it was always on the cards. I have to say, that I did pick Wales by 7. Cheers, and good picking.
    
    9 years ago
    - Jaco Griesel
      
      Mark, I hear what you’re saying. The thing with the Six Nations competition is that any of those teams can win on the day (even Italy has provided an upset or two in the past).
      
      But on this day, with all the things going in favour of England (Twickenham, England RWC2015, Six Nations results, injured Wales players, etc.) the expectation surely was that England only needed to show up for 80 minutes. And it almost worked for them – Wales scored a try in the final ten from what could easily be described as a lucky bounce of the ball, England went for a try instead of kicking for goal (and failed in getting any points), and Wales slotted a penalty kick from a rather difficult field position.
      
      On SuperBru, only 16% of the Brus predicted that outcome – a major upset, then.
      
      Now, Prof Scott is predicting that England will beat Australia. From where I’m sitting and based on current form, that might also be seen as a major upset. This might just be the game of the tournament! I’ve made all my picks for this round, but this is the one that I’m not sure about. There are just too many factors that can screw things up! ;-)
      
      9 years ago
Xavier Wing

Hi David,

I stumbled upon your predictions and wanted to start learning how to make my own predictions statistically. What would I need to acquire knowledge in? I have read your basic method but still am still confused as I dont come from a maths background.

9 years ago
- David Scott
  
  The method is simply the error-correction form of exponential smoothing, plus home ground advantage. You need a basic understanding of time series forecasting and the ability to carry out repetitive numerical calculation. It could be done in Excel, but that would be tedious and error-prone. I program in R.
  
  You also need to be able to assemble years of data to initialise ratings and to enable appropriate choice of parameters. That usually requires data munging ability because entering data by hand is also tedious and error-prone.
  
  9 years ago
Llewellyn Wepener

Any predictions for Sundays games.
4th October

9 years ago
- David Scott
  
  Available now
  
  9 years ago
darren seath

Hi David, what is your prediction for tonights game Canada Vs Romania? Cheers

9 years ago
David Vin

The question is are the All Blacks holding back ?

9 years ago