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Duckworth–Lewis method

Written By Admin on Thursday, 7 June 2012 | Thursday, June 07, 2012

The Duckworth Lewis method or D/L method is a set of formulas and tables created by Frank Duckworth and Tony Lewis. The method was adopted by the International Cricket Council (ICC) to address the problem of delayed one-day cricket matches for reasons of rain, poor light and floodlight failures although it has also been used in events that have been shortened due to crowd problem, sandstorms and even snowstorms.

It was first used in international cricket in the second game of the 1996—97 Zimbabwe versus England One Day International series, which Zimbabwe won by seven runs, and was formally adopted by the International Cricket Council in 2001 as the standard method of calculating target scores in rain shortened one-day matches.

Various different methods had been used previously, including run-rate ratios, the score that the first team had achieved at the same point in their innings, and targets derived by totaling the best scoring over’s in the first innings. All these methods have flaws that are easily exploitable; for example, run-rate ratios take no account of how many wickets the team batting second have lost, but simply reflect how quickly they were scoring when the match was interrupted; so, if a team felt a rain stoppage was likely they could attempt to force the scoring rate without regard for the corresponding highly likely loss of wickets, skewing the comparison with the first team.

The most notorious example is the "best-scoring overs" method, used in the 1992 Cricket World Cup. Before a brief rain interruption, South Africa was chasing 22 runs from 13 balls to win, but following the stoppage, their target was amended to 21 runs from one ball (a reduction of only one run compared to a reduction of 12 balls, and the maximum score from one ball is generally six runs). The D/L method avoids this flaw: in this match, the revised D/L target would have been four runs to tie or five to win from the final ball.

The essence of the D/L method is 'resources'.

Each team is taken to have two 'resources' to use to make as many runs as possible: the number of overs they have to receive; and the number of wickets they have in hand. At any point in any innings, a team's ability to score more runs depends on the combination of these two resources. Looking at historical scores, there is a very close correspondence between the availability of these resources and a team's final score, a correspondence which D/L exploits.

Using a published table which gives the percentage of these combined resources remaining for any number of overs (or, more accurately, balls) left and wickets lost, the target score can be adjusted up or down to reflect the loss of resources to one or both teams when a match is shortened one or more times. This percentage is then used to calculate a target (sometimes called a 'par score') that is usually a fractional number of runs. If the second team passes the target, then the second team is taken to have won the match; if the match ends when the second team has exactly met (but not passed) the target (rounded down to the next integer) then the match is taken to be a tie.

This method can only yield a result only if both the teams bat for a minimum of 20 overs in a one-day international and a minimum of 5 overs in a T 20 match.

D/L method is split into two types, one being called syandard edition and other Professional. While the standard method is easy to interpret and can be assessed using pen and a paper, a professional edition requires a computer to calculate the target.

ICC has adopted the Professional edition since 2004.

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