Ever wondered how a score target is set for the team batting second after the match was interrupted by rain? The method, which is used to ascertain the score, is a mathematical formulation devised by two statisticians Frank Duckworth and Tony Lewis in England. As the method came under the custody of Professor Steven Stern, it is known as the Duckworth-Lewis-Stern method or DLS method.
The method was devised to set a fair target for the second team's inning with the same level of difficulty as the target scored in the first inning.
Each team in a match, except Test cricket, has two resources available with which to score runs, i.e, overs to play and wickets remaining. The target is adjusted equally to the change in the combination of these two resources.
The Calculation
The method is based on "resources" used by the teams to score runs. During any inning, the ability to score more runs depends on these two resources. The DLS method converts combinations of overs and wickets left into a percentage figure (with 50 overs and 10 wickets = 100%), and these are all stored in a published table. The target for team 2 can be adjusted from the total the team batting first achieved using these percentages, to reflect the loss of resources to teams when a match is halted.
Let's take an example. India batted first against Pakistan and scored 328 all out in a one day international in February 2006. Pakistan was 7 wickets down and scored 311 after 47 overs when the play was stopped. Now, how to ascertain who won the match or how much runs Pakistan needed once the play resumed?
According to the method, Pakistan losing the final three overs is proportionate to a loss of 7.3% of resources by the Duckworth-Lewis tables available at the time, making a tie.
T= 328 x (1.00 - 0.073)
= 304.5
In order to win, Pakistan needed more than 304. As the team already scored 311, Pakistan was declared the winner by 7 runs.
Changes in method
The method is reviewed every three years and in 2004, a special Professional Edition was introduced where computers are used. The Standard Edition is still used in lower-level matches, which is a published list of tables.
The method was almost successful until the 2003 World Cup when South Africa failed to progress to the second round on home soil after they miscalculated the score.
