The Duckworth-Lewis-Stern approach, or DLS method as it is now known, is a mathematical framework used to determine target scores and results in limited-overs games that are shortened by rain. It was created by English statisticians Frank Duckworth and Tony Lewis and was first applied in 1997. Prior to the 2015 World Cup, Australian professor Steve Stern modified the formula and took on the role of custodian, adding his name to the title. It plays a significant part in determining the outcome for the team batting second in a limited-overs cricket situation.
How does Duckworth-Lewis-Stern work?
The DLS technique adjusts the target based on the availability of resources, taking into account both wickets and overs as resources. A side has 50 overs and 10 wickets available at the beginning of an innings, which is 100 percent of its resources. The number of balls and wickets left at any given time is expressed as a percentage using the DLS method.
What percentage value does a wicket or a ball have? This is determined using a method that analyses statistics (ODI and T20, men's and women's) from a sliding four-year window and takes into account the score pattern in international matches. The DLS changes when score trends change since a new year's worth of data is uploaded on July 1 of every year.
Par Score and Target Score
The target score is the amended score that a team must achieve after an interruption. The par score is the total that a chasing team should have reached when they are "X" wickets down at the time of interruption. While the par score varies depending on how many wickets are lost, the target score is a set figure. Prior to an interruption, the par scores are computed, whereas the set goals are determined after an interruption.
By estimating how many runs teams should have scored—and would have scored—if the resources available to both sides were equal, the DLS technique determines targets and results. The formula can be written simply as follows to calculate a target: Team 1's score multiplied by (Team 2's resources / Team 1's resources) gives Team 2's par score.
In international cricket, a computer programme is used to determine the resource values, which are not made available to the general public.
It has long been believed that teams chasing high totals using the old D-L technique were better off keeping wickets when rain was imminent, even if it meant scoring at a slower rate. By altering the algorithm to account for the changing reality in high-scoring ODIs and T20 matches, Steve Stern felt he had improved on the D-L technique in this regard.
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Featured photo: Marty MELVILLE / AFP