It is much more complex than that.
1. How are the ratings calculated?
After every Test series, the two teams receive a certain number of points, based on a mathematical formula. Each team's new points total is then divided by its new match/series total to give an updated rating. With batting averages, if you are dismissed in your next innings for more than your average, your average will increase. Conversely, scoring less than your average will cause it to fall. Similarly, under the Reliance ICC Test Championship method, the points earned from a Test win will always be more than the rating the team had at the start of the series. Equivalently, a team losing a Test match will always score fewer points than its rating. So a win will always boost a team's rating and a defeat will harm it.
A draw between a higher and lower rated team will slightly benefit the rating of the lower rated team at the expense of the higher rated team. A draw between two similarly rated teams will leave both their ratings unchanged. A tied match is treated the same as a draw for rating purposes.
2. What does a particular rating signify?
A team that, over the period being rated, wins as often as it loses while playing an average mix of strong and weak opponents will have a rating of close to 100. A rating of 100 could also correspond to a side that wins more often than it loses but who has generally played more matches against weak teams. Similarly, if the majority of its matches are against strong teams, then a rating of 100 could be achieved despite having more defeats than victories. It is quite often the case that there are a number of teams in the 90-110 range. These teams are of broadly similar standard. A rating above 120 suggests consistently strong performances. Above 130 is rarely achieved and suggests a high degree of dominance over all other teams.
In every match the total rating points available equals the sum of the initial rating of the two teams, so ratings can be thought of as being redistributed rather than created. There is therefore no 'inflation' in this rating system, so a rating of 120 suggests the same degree of superiority over opponents now as in the past or future, and a team can meaningfully compare its rating movements over time.
3. How quickly do ratings change?
The amount by which a rating improves after winning a Test will depend on the rating of the opponent. A win over a much stronger team (i.e. one with a much higher rating) boosts the rating more than beating a much weaker opponent. Conversely, losing to a much stronger team will not cause the rating to drop too far, but losing to a weaker side would.
It is possible for a team to win a series yet for its rating to fall. This will happen if a stronger team wins a series but by a smaller margin than the respective ratings suggest should be the case. For example, when Australia played England in a five-Test series in 2002-03, Australia needed to win by a margin of at least three Tests just to maintain its very high rating.
4. How is the series result incorporated?
At the end of any series comprising two or more Tests, a series bonus will be awarded. Like an individual Test match, a series can be won, drawn (tied) or lost. For rating purposes, the series result is equivalent to the result of one further Test. To explain, suppose a team has just won a Test series. The series bonus can be regarded, for rating purposes, as if one extra Test has been played and won by the team that has just won the series. If a series finishes level, the series bonus is equivalent to the two teams playing an extra drawn Test.
5. What period does the table cover?
The table reflects all Test series completed since the annual update made three to four years previously. This pattern is repeated each May, with the oldest of the four years of results removed to be gradually replaced with results of matches played over the following twelve months. Thus once a year, the rankings will change overnight without any new Tests being played. This process, called updating the data, takes place at the start of May each year. This time has been chosen since it is usually a relatively quiet time in the international calendar. Before 2012, the annual update took place in August.
6. How are the results weighted?
All matches included within the Reliance ICC Team Rankings Tables will always fall into one of two time periods:
* Period One covers the earliest two years of matches
* Period Two covers all subsequent series, i.e. the past one to two years
Weightings are applied to these two groups of series so that the ratings more fully reflect recent form. The weightings are as follows:
* Period One matches have a weighting of 50 per cent.
* Period Two matches have a weighting of 100 per cent.
In the current table, series completed since last May receive a weighting of 100 per cent. After next May, the weighting of series being played now will remain at 100 per cent, while the weighting of series played in the previous year will fall to 50 per cent.
The 'match/series total' column in the Reliance ICC Test Team Rankings table comprises a combination of individual Tests and series. This total along with the number of points earned in each period is multiplied by the weighting factor. For example, suppose a team played 20 Tests and six series in Period One, plus 15 Tests and five series in Period Two. The total matches played for rating purposes is 50 per cent of (20+6) plus 100 per cent of (15+5), which equals 33. (A small technical adjustment ensures that, for all teams, the total number of matches and rating points is always a whole number.)
