Ranking World Rugby
World Rankings show a team's form relative to its international rivals as it enters the World Cup and is an indication of how far a team will likely progress. The system behind the rankings is explained below.
All 95 member unions of the International Rugby Board (IRB) have a points rating, typically between zero and 100. The ranking represents the overall performance of national rugby teams competing at the international level. New Zealand is presently the highest ranked team with a rating of 93.38 points. Australia is the second highest ranked team with a rating of 87.03. Ireland is ranked fifth in the world with 81.42 points.
Rankings are calculated using a points exchange system – any points gained by a winning team will be lost by the losing team. A winning side always increases its rating and a losing side always decreases its rating. The number of ranking points won or lost by a team depends on its ranking relative the opposing team - should a higher ranked team win, it will gain less points than if the lower ranked team wins.
The number of points won or lost by a team is calculated by taking the difference in ranking points between the teams (e.g 6.35 between New Zealand and Australia) and consulting a sliding scale (see chart opposite). In this instance, New Zealand would gain 0.365 points were it to win; Australia would gain 1.635 points if it won.
Where a side wins a match by more than 15 points, the number of points gained by the winning side is multiplied by 1.5. This is to account for winning ‘with something to spare'. The losing side is deducted the same number of points. The tolerance for margin of victory is set to 15 points because research conducted by the IRB suggested that ‘match results are more important than margins of victory' in producing accurate rankings – a win by 60 point s or 100 points against lower-rated opposition is not a good indicator of future performance.
Home advantage is negated by treating the home nation as though they are three rating points better than their current rating. This effectively ‘handicaps' the home side as they will tend to pick up fewer points for winning and give away more points for losing. In the event of a draw, a side's rating will move toward the opponent's rating, taking home advantage into account. Points exchanges are doubled for World Cup games ‘to recognise the unique importance of this event', but all other international matches are treated equally.
The excange of points may be illustrated using the recent test match between Scotland and Ireland in Edinburgh on 11 August.
Step 1) Check pre match ratings
The top 11 countries in the IRB World Rankings immediately before the match are shown to the right. Scotland was on a rating of 73.94 and Ireland was on 82.52, a difference or rating gap, of -8.58. Adding three points to take Scotland's home advantage into account, the rating gap becomes -5.58.
Step 2) Check the Core Rating Change
Checking the possible Core Rating Changes from the chart we see that in the event of a draw, a Core Rating Change of 0.558 points would be gained and lost by Scotland and Ireland respectively. In the event of a home win, Scotland's rating would increase and Ireland's would decrease by 1.558 points. Should Scotland lose, Ireland would gain and Scotland would lose 0.442 points. And should either side win with more than 15 points ‘to spare', multiply the Core Rating Change by 1.5.
So Ireland, as the higher rated side (allowing for Scotland's home advantage) would pick up fewer points than Scotland if they won the match, and would give away more points if they lost.
Step 3) What happened
Scotland won the match 31-21 so the sides exchanged 1.558 rating points, with Scotland going up to 75.50 and Ireland going down to 80.96. The updated top eleven ranked teams after the weekend of play appeared as above. Neither Argentina nor Samoa had a game that weekend (hence no change in points ), so when the rankings were recalculated Ireland dropped one place in the rankings to sixth position behind Argentina, while Scotland rose to tenth position ahead of Samoa.