RWC 2023 Predictions for Week 1

Team Ratings for Week 1

A long time coming but here are my predictions. No doubt many will disagree with my initial ratings. I try as far as possible to simply rely on data and avoid subjective judgements, and these ratings follow that rule as far as I have been able.

In this case I have had to make a number of decisions regarding ratings which are not based on data but my knowledge of the game, because the schedule of international games prior to the RWC is not like a normal league competition, where all teams play every other team pretty much the same number of times (AFL is actually a mild exception to this rule where some teams play each other once and others twice). The number of games any two teams in the RWC play each other prior to the Cup varies wildly. The European teams play each other regularly each year, while other teams have never played each other. (Chile and Portugal have never played the All Blacks as far as I am aware.) So my normal practice of starting at some early time point with all teams rated equal and running predictions forward and adjusting ratings up to the present time is not going to work when some teams never play or rarely play the top nations. As a consequence, my ratings are a bit of a hybrid. For the top 10 nations (the obvious suspects including Argentina and Italy), the ratings are based on all international games involving those countries from the end of RWC 2019 to now. For the remaining 10 countries, I arbitrarily set the initial ratings of Fiji, Samoa, Tonga, Georgia, and Japan to be -10, Romania to be -15, and Chile, Portugal, Uruguay and Namibia to be -20, before running through all games they played against any other RWC 2023 finalists up to the present time. These choices were not entirely without any basis. For competitions where I have given predictions over a number of years, when a new team is added to a competition or a team is promoted, I have usually assigned a rating of -10 and found that works reasonably well.

Finally after combining the ratings, I have rescaled so that the average rating is 0.

Any informed follower of rugby may reasonably wish to make accommodation for factors they consider important: the recent change to eligibility allowing Pacific Island teams to include the likes of Charles Piutau is an obvious one.

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Predictions for Week 1

Here are the predictions for Week 1. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.