Why Australia, Sri Lanka and West Indies are in one group

How the groups were made ? ICC World Twenty20 2009

The 12 teams competing in this year's World Twenty20 are the nine Full-Member countries and three Associates who made it to England through the qualifying tournament, which was held in Belfast. They have been divided into four groups of three each based on their seeding, which depended on their standings in the inaugural World Twenty20 in 2007 (for the teams that took part in it). Since India were champions they were seeded first, their opponents in the final, Pakistan, were ranked second, while the losing semi-finalists Australia and New Zealand were seeded third and fourth. The top four seeds were then put in four different groups for this year's tournament.
The best among the rest, South Africa, were seeded fifth and put in the same group, D, as the team seeded fourth -New Zealand - while Sri Lanka and England, the 6th and 7th seed, were placed in groups C and B. Had West Indies at least finished eighth in 2007, there would not have been a 'group of death' this year. But they did not even win a single game, losing to Bangladesh because of an inspired innings from Mohammad Ashraful, and were seeded 11 and placed in Group C. Bangladesh, who qualified for the Super Eights in 2007 but didn't win a game in that round, were eighth and put in India's group.
Group A - India (1), Bangladesh (8), Ireland (9) Group B - Pakistan (2), England (7). Netherlands (10) Group C - Australia (3), Sri Lanka (6) West Indies (11) Group D - New Zealand (4), South Africa (5), Scotland (12)
Each team will play the other in its group during the preliminary round and the top two will qualify for the Super Eights. What this means is that either Bangladesh or Ireland, or both, are assured of a place in the second stage, while one of Australia, Sri Lanka and West Indies will crash out after round one, leading to the possibility of another group of death in the next World Twenty20, in the Caribbean in 2010.
If two teams in a group have equal points at the end of the first round, the one with more wins will be placed higher. If they have equal points and the same number of wins, a likely scenario, then the team with the higher net run-rate will be ranked higher. Should net run-rate also fail to separate the sides, then the one with the higher number of wickets taken per balls bowled in the group stage in which results were achieved, will be preferred. And if the teams remain in a deadlock, then the winner of the group match between the sides will prevail. If all of the aforementioned tie-breakers fail, the teams will be separated by drawing lots.
And should the weather in England wreck all the three matches of a particular group, the top two seeded teams in the group will progress. No points, however, will be carried forward from the group stage into the Super Eights.
The Super Eights
The teams in the Super Eight will be designated as A1, A2, B1, B2, C1 C2, D1, D2 depending on which group they qualified from. If the top two seeds from a group qualify, they will be seeded 1 and 2 respectively for the Super Eight regardless of which team actually finished first and second in a group during the first round. For example, if Bangladesh are first and India are second in Group A, Bangladesh will still be A2 while India will remain A1 for the Super Eight because India were seeded 1 while Bangladesh were 8. However, if the third seeded team in the group knocks out a higher seed, it will take the place of the knocked-out opponent. For example, if Bangladesh and Ireland qualify from Group A, then Ireland will be A1 for the Super Eight stage. If India and Ireland qualify, then Ireland will be A2.
During the Super Eight, the teams will be split into two groups of four - A1, B2, C1 and D2 are in the first group, while A2, B1, C2 and D1 are in the second. Each team will play the others in its pool with the top two from each group qualifying for the semi-finals. If teams are tied on points in a Super Eight group then the same parameters which were used to break a tie in the preliminary stage will be used, the difference being that only the Super Eight matches will be taken into consideration for most wins, net run-rate etc.
If all of the matches of a Super Eight group are ruined by rain, the teams will be ranked on basis of most points, most wins, net run-rate during the group stage and the top two will go through. If the teams still cannot be separated the semi-finalists will be picked based on the original seeding for the tournament.
A one-over eliminator, or Super Over, will be used to break a tie in a semi-final, if one should occur. However, if weather prevents the Super Over from taking place after a tie, the team which progresses to the final will be determined by looking at who has the most wins, better net run-rate, higher number of wickets per balls, the only difference being that this time both group and Super Eight matches will be taken into consideration.
The final, however, has no such provisions. If the final is tied, the match will be decided by a one-over eliminator. If the eliminator cannot take place because of bad weather, then the two finalists will be declared joint winners.

Source:
George Binoy is a senior sub-editor at Cricinfo