Rules
The system ensures that it is representative of the teams' performance despite playing differing numbers of matches per annum, and the differing strength of opposition that teams have to face. The factors taken into account are as follows:
- Match result
- Match status
- Opposition strength
- Home advantage
- Match result
For each match played points exchanges are awarded for the following five outcomes and was developed using results of international matches from 1871 to the present day:
- a win or loss by more than 15 points
- a win or loss by up to 15 points
- a draw
Match status
Different matches have different importance to teams, and World Rugby has tried to respect this by using a weighting system, where the most significant matches are in the World Cup Finals. Points exchanges are doubled during the World Cup Finals to recognise the unique importance of this event. All other full international matches are treated the same, to be as fair as possible to countries playing a different mix of friendly and competitive matches. Matches that do not have full international status do not count.
Opposition strength
A win against a very highly ranked opponent is a considerably greater achievement than a win against a low-rated opponent, so the strength of the opposing team is a factor. Thus match results are more important than margins of victory in producing accurate rankings. This is because when a highly ranked team plays a lowly ranked team and manages to beat them by over 50 points, it does not necessarily indicate how either team will perform in the future.
Home advantage
When calculating points exchanges, the home side is handicapped by treating them as though they are three rating points better than their current rating. This results in the home side gaining fewer points for winning and losing more points for losing. Because of this, any advantage that a side may have by playing in front of their home crowd is cancelled out.
New and dormant nations
All new member nations start with 30.00 points, which is provisional until they have completed ten test matches. When countries merge, the new country inherits the higher rating of the two countries but when they split (e.g., the planned 2010 breakup of the Arabian Gulf rugby union team into separate teams representing its current member countries), the new countries will inherit a rating at a fixed level below the rating of the original country.
Before 1 December 2012 new member nations were given 40.00 points.
Countries that have not played a test for two years are removed from the ranking system and the list. If they become active again, they resume their previous rating.