It’s quarter-final week at the 2023 Rugby World Cup (RWC). The quarter-final match-ups are (1) Wales v Argentina, (2) Ireland v New Zealand, (3) England v Fiji, and (4) France v South Africa. Which of those teams is most likely to win the tournament?
As others have explained, the probability of each team progressing in the tournament can be calculated using a suite of statistical models known as Rugby Vision. The models have accurately predicted outcomes at previous RWCs.
Global rugby rankings
A key component of the modelling system is a rating system for international rugby teams. The Rugby Vision Global Rugby Rankings are a custom ‘points exchange’ system based on past game results and home advantage (if applicable). After each game, the team that performed better than expected gains rating points and the team performed worse than expected loses rating points.
The system has some similarities with the official World Rugby Rankings, but a key difference is that the Rugby Vision Global Rankings are less sensitive to the outcome of any particular game.
Current Rugby Vision Global Rankings and ratings points for the 20 teams that qualified for the 2023 RWC (the eight quarter-finalists and the 12 teams eliminated in the pool stage) are displayed below. New Zealand is the top-ranked team followed by South Africa, Ireland, and France. The same four teams make up the top four in the official rankings, but the seedings are different. Currently, the official world rankings have Ireland at the top, followed in order by France, South Africa, and New Zealand.
Predicting game results
In the Rugby Vision rankings, differences between rating points for any two teams equal the predicted score margin for a game played at a neutral venue, and home advantage (if applicable, in this case only for France) is worth 5.5 points. This means that in the Wales v Argentina quarter-final, Argentina is expected to win by 111.28 – 110.41 = 0.87 points, or 1 point when rounded to the nearest whole point. Thus, it is predicted to be a close match. The Rugby Vision system goes further: it specifies a probability distribution for possible score margins. In this case, it says that there is 52.6% chance that Argentina will win the game, and a 47.4% chance that Wales will win. (NB: There are no draws in the knockout stages of the Rugby World Cup. Instead, there are two 10-minute periods of extra time which, if they don’t produce a clear winner, are followed by a 10-minute period of sudden death).
To account for uncertainty in game outcomes, the system simulates the RWC 10,000 times in accordance with tournament rules. Estimated probabilities of each quarter-finalist reaching various stages of the 2023 RWC are shown below. The estimated probabilities are influenced by team rating points (including home advantage for France), and the scheduling of knockout matches.
Despite being the sixth-ranked side, England is the most likely team to make the semi-finals as they play tenth-ranked Fiji in their quarter-final, while each top-four side plays another top-four in other quarter-finals.
Beyond the quarter-final, England have only a 13.6% chance of making the semi-finals, and a 2.8% chance of being champion. This is because, if England qualify, they will play either France or South Africa in a semi-final, and likely New Zealand or Ireland in the final. Ultimately, the draw makes it easier for some teams to qualify for the semi-finals, but it does not have a large impact on who will win the RWC.
The teams with the highest probability of being crowned world champions are New Zealand (37.0%), South Africa (22.2%), France (20.2%), and Ireland (15.7%). This ranking closely matches the ordering of the top four teams in Rugby Vision’s Global Rugby Rankings.
The final whistle
Rugby Vision’s predictions provide a reliable forecast of likely RWC outcomes but unlikely results are expected from time to time, we just don’t know when upsets will occur. Who will win the 2023 RWC? New Zealand have a higher chance of winning (37%) than any other team, but that also means that there’s a 63% chance another team will be 2023 RWC champions.
Niven Winchester is a professor of economics at the Auckland University of Technology, and a senior fellow at Motu Economic & Policy Research.