They’re the favourites but . . .
The All Blacks are the most likely team to lift the Webb Ellis Cup in Yokohama on November 2. But it’s even more likely that any one of a number of other teams will deny them their third world crown in a row.
Stuff today launches its
Rugby World Cup Power Rankings, days out from the start of the tournament.
The Power Rankings use four decades of international rugby results to give each team a rating that reflects their strength relative to the other teams.
Taking the ratings and the fixtures into account, it forecasts each team’s chances of advancing to various stages of the tournament, and of ultimately lifting the Cup.
It also forecasts the outcome of each game. Rather than trying to ‘‘pick’’ a winner, the game forecasts show each team’s probability of winning based on the difference in rating between teams.
After each game is played, ratings will change based on the result and the points margin. New ratings will then be used to update the forecasts for every team and every remaining match.
Leading into the tournament, the Power Rankings give the All Blacks a 34 per cent chance of World Cup victory and a 50 per cent chance of making the final.
The chasing group is led by England and Ireland, who both rate about a 20 per cent chance of lifting the Cup.
The Power Rankings forecasts rate England, Ireland and Wales as a better chance than South Africa, who currently rate only a 9 per cent chance, despite winning the Rugby Championship and performing well in 2019.
That’s partly a function of their difficult route to the semifinals: they face the All Blacks in the group stage and if they lose that (the forecast puts that at a 66 per cent chance) would most likely face a quarterfinal against Ireland. And it’s also to do with how the rating system works.
South Africa’s rating fell steadily between 2015 and 2018. While their good form has boosted them this year, it has not yet been sustained for long enough to lift their rating back level with the likes of Ireland and Wales, who have all had sustained periods of good form since 2015.
It could be that South Africa are the real deal, but the system is not yet convinced. It needs more evidence before it boosts South Africa’s chances.
This can be a weakness of the system in the short-term when a team suddenly goes from being bad to being very good, but it’s also a strength in that it does not get sucked into thinking a team that has a few good results are better than they really are.
Luckily for our forecast, South Africa face the All Blacks in their opening game. If they win, it will be further confirmation that their recent form really is more than a blip and their rating and chances of winning the World Cup will increase significantly – the best way to boost your rating is to beat a team with many more rating points.
Historically, the winners of the World Cup have shown gradual ratings improvement throughout the four-year period in the lead-up to their triumph. Examining the winning 2003 England team (in red on the graph below), for example, shows their victory was no fluke. England showed steady improvement right up until their only World Cup triumph.
The champion Australian and South African teams showed similar ratings improvement in their tournament run-ins.
For the successful All Blacks teams of 2011 and 2015 it was more a case of maintaining their superior rating. It’s hard for the top team to improve their rating too much.
The 1987 World Cup is near the beginning of the period covered by the Power Rankings, so the All Blacks had not had much time to build up a rating that reflected their true strength.
The Power Rankings are an Elo rating system. Elo has been used to gauge the relative strengths of players and teams in many different sports. All teams are given an initial rating and these are then updated as games are played. Winners take ratings points off the losers making it a zero-sum system.