New Zealand fans can find solace in statistical modeling that predicts the All Blacks as the favorites to win the 2023 Rugby World Cup (RWC) despite their recent record loss to South Africa in August. According to Rugby Vision, an algorithm specifically designed to predict outcomes for major rugby competitions, New Zealand has a 33.5% chance of securing their fourth RWC title. Following closely behind are South Africa (26.2%), France (20.6%), and Ireland (11.9%).
The accuracy of the model has been evaluated based on its past predictions for previous RWCs, and it has been found to be highly reliable. Unlike the official world rugby rankings, the Rugby Vision model is less affected by the outcome of individual games. It operates using three main components: an international team rating system, estimation of expected outcomes for RWC games using these ratings, and 10,000 simulations of the tournament to account for uncertainty.
The Rugby Vision rankings utilize a unique “points exchange” system that incorporates past game results and home advantage. After each game, the team that performs better than expected gains rating points, while the team that underperformed loses rating points. The current rankings for the 20 teams that have qualified for the 2023 RWC show New Zealand at the top, followed by South Africa, Ireland, and France. Although the top four teams remain the same in the official rankings, the seedings differ.
The Rugby Vision rankings determine the score margin between two teams based on their rating points. A home advantage, if applicable, is worth 5.5 points. For instance, in the opening game between France and New Zealand, held in Paris, New Zealand is expected to win by three points. This estimate is derived from the difference in rating points between the two teams (128 minus 119.5) plus 5.5 for France’s home advantage. On average, if the game was played 100 times, New Zealand would win by three points in 57 games, France would win 40, and three games would result in a draw.
To account for uncertainty in game outcomes, the Rugby Vision model simulates the RWC 10,000 times in accordance with tournament rules. Through these simulations, the model estimates game results, bonus points, finishing positions, and the winner of knockout matches.
Looking ahead to the 2023 RWC, Pool A is highly likely to see New Zealand and France emerge as quarterfinalists. In Pool B, South Africa and Ireland have a strong chance, but Scotland may pose a threat. Pool C is anticipated to be the most balanced, with Australia and Wales as frontrunners, though Fiji also has a reasonable chance of advancing. In Pool D, England and Argentina are favorites, but Japan and Samoa could potentially disrupt these predictions.
Following the initial round, the quarterfinals will see teams from Pool A competing against those from Pool B. Due to the perceived strength of these pools, the semifinalist probabilities for these teams are relatively low. For example, Ireland has an 81.2% chance of reaching the quarterfinals but only a 33.1% probability of progressing to the semifinals. Conversely, teams in Pools B and C have easier quarterfinal opponents, resulting in England being the second most likely team to make the semifinals despite their relatively low ranking.
In the semifinals, teams from Pools A and B will face teams from Pools C and D. Because of the predicted superiority of teams from Pools A and B, their chances of reaching the final are only slightly lower than their chances of reaching the semifinals. Conversely, despite high semifinalist probabilities, teams from Pools C and D have relatively low finalist probabilities. For instance, England has a 55.0% chance of reaching the semifinals but only a 9.7% chance of making it to the final.
While the Rugby Vision predictions provide a reliable forecast, upsets can still occur, adding intrigue to the sport.