How do the ICC Test ratings work?
The rating system is based on assigning points to teams for every Test match played, and then averaging it out over all Tests played by the team during the period under consideration. The final rating is thus an average score for the team during that period.
The points awarded to a team depends on the strength of the opposition. A win against a stronger opposition counts for more than a win against a weak opposition. The strength of the opposition is determined by their rating points at the start of the series, and updates happen only at the end of a series, not after each Test.
Is there a bonus for winning a series?
Yes, a series win counts as an extra Test match won. So, if a team wins a series 2-1, when assigning points it will count as a 3-1 win.
Does an away win count for more than a home win?
No, there is no extra weightage given to an away win; only the opposition strength is taken into account.
Does a team's rating get affected if it sends a second-string team for a series?
No, the only number that is taken into account is the team's rating points at the start of the series. If the opposition beats a team which is weakened by a few withdrawals, it will still get the same points as it would have beating the full-strength team.
How does the calculation work in a series?
Each team gets one point for a Test win, 0.5 points for a draw, and an extra point for a series win. Thus, if Australia win a five-Test Ashes series 2-1, they will get 4 points, while England will get 2.
The method for calculating the rating points in a series depends on the relative strengths of the two teams playing that series. If the difference in rating points between the two teams at the start of the series is less than 40, then each team gets:
The team's series points (4 for Australia in the above example) multiplied by 50 points more than the opposition's rating points, plus
The opposition's series points (2 in the above example) multiplied by 50 points less than the opposition's rating points.
If the difference in rating points between the two teams at the start of the series is 40 or more points, then the stronger team gets:
The team's series points multiplied by 10 points more than the team's own rating, plus
The opposition's series points multiplied by 90 points less than the team's own rating.
The weaker team gets:
The team's series points multiplied by 90 points more than the team's own rating, plus
The opposition's series points multiplied by 10 points less than the team's own rating
This series score is added to the team's previous total ratings points, and divided by total number of matches plus series played to arrive at an average score for the team, which is their rating points.
What is the time period considered?
A minimum of 36 months, and a maximum of 48 months. Every May, the results from months 37 to 48 drop off. For example, in May 2015, the time period considered is May 2012 onwards, with results from May 2011 to April 2012 dropping off. Till April 2016, this is the time period considered; in May 2016 all results between May 2012 and April 2013 will be knocked off.
How are the older results weighted compared to the more recent ones?
The first two years get 50% weightage, while the last 12 to 24 months gets 100% weightage. For example, in May 2015, all matches from May 2012 to April 2014 gets 50% weightage, while matches after May 2014 gets 100% weightage.