Duckworth–Lewis method

The Duckworth–Lewis (D/L) method is a mathematical formulation designed to calculate the target score for the team batting second in a limited overs cricket match interrupted by weather or other circumstances. It is generally accepted to be the most accurate method of setting a target score. The D/L method was devised by two English statisticians, Frank Duckworth and Tony Lewis. After their retirements Professor Steven Stern became the custodian of the method. In November 2014, it was renamed the Duckworth–Lewis–Stern method (or D/L/S method).

The basic principle is that each team in a limited-overs match has two resources available with which to score runs: wickets remaining, and overs to play. Where overs are lost, setting an adjusted target for the team batting second is not as simple as reducing the run target proportionally to the loss in overs, because a team with ten wickets in hand and 25 overs to bat can be expected to play more aggressively than if they had ten wickets and a full 50 overs, for example, and can consequently achieve a higher run rate. The Duckworth–Lewis method is an attempt to set a statistically fair target for the second team's innings, based on the score achieved by the first team, taking their wickets lost and overs played into account.

Various different methods had been used previously to resolve rain-affected cricket games. The most common were the average run-rate method, and the most productive overs method.

The average run-rate method had been replaced in the early 1990s by the most productive overs method, developed by Australians after a 1989 World Series final between Australia and the West Indies. Chasing Australia's 226/4 off 38 overs, the West Indies needed 180 off 31.2 overs. Rain stopped play for one hour and 25 minutes, and under the average run-rate method, the revised target was 61 runs off the 11.2 overs that remained. The West Indies won the match and the competition with 4.4 overs remaining and eight wickets in hand. Australian fans booed this unsatisfactory conclusion, which was criticised by the media and Australia's captain. In this match, the D/L method would have increased the West Indies' target to 232 to take into account a two-hour rain delay during Australia's innings, and then revised the target to 139 after the second interruption.

The D/L method was devised by two British statisticians, Frank Duckworth and Tony Lewis, as a result of the outcome to the semi-final in the 1992 Cricket World Cup between England and South Africa, where the most productive overs method was used. Rain stopped play for 12 minutes with South Africa needing 22 runs from 13 balls chasing England's 252/6 off 45 overs. The revised target left South Africa needing 21 runs from one ball, which was a reduction of only one run compared to a reduction of two overs, and a preposterous target given that the maximum score from one ball is generally six runs.

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