D/L method: answers to frequently asked questions (updated December 2008)
by Frank Duckworth & Tony Lewis
(Note: throughout the following, the side which bats first is called Team 1 and the side batting second is called Team 2.)
1. What is the difference between the Standard Edition and the Professional Edition?
At the top level of the game, the Professional Edition of the D/L method is now used. This requires use of a computer program. At lower levels of the game, where use of a computer cannot always be guaranteed, the Standard Edition is used. This is the method which was used universally before 2004; it is operated manually using the published tables of resource percentages.
2. Why should Team 2 sometimes be set the task of scoring more runs than were made by Team 1 when they have the same number of overs to face?
When the interruption occurs during the first innings, so that the match is shortened to one of fewer overs per side than it was at its start, Team 1 are usually more disadvantaged than Team 2. Before the stoppage they had been pacing their innings in the expectation of receiving say 50 overs and would not have taken the risks of scoring as fast as they would have done had they known their innings was to be shortened. Team 2, on the other hand, know from the start of their innings that they have the reduced number of overs and can pace their entire innings accordingly. Team 2 are set a higher target to compensate Team 1 for this disadvantage.
Consider, for example, when Team 1 have batted for 40 of an intended 50-over innings and then rain washes out the rest of their innings and there is just time for Team 2 to receive 40 overs. If they had wickets in hand, Team 1 might have expected to make around 60 or 70 in those final 10 overs. But Team 2 know they have only 40 overs to receive from the moment they start their innings. The average score in a 40-over innings is only 20 to 25 less than that made in 50 overs, so Team 1's loss is typically 40-45 runs greater than Team 2's and the target is raised by about this amount.
The necessity to set a higher target for Team 2 arises from the regulations for most competitions that require that lost overs, where possible, be divided equally between the two sides. It would be possible to compensate Team 1 for their disadvantage by allowing them to face more overs than Team 2 and in this way the latter need not be set an enhanced target, but this would require a complicated calculation and would reduce the scope for accommodating further stoppages. Because of these disadvantages, cricket authorities have preferred to stay with the present regulations.
3. Why should this apply when Team 1 have been bowled out?
In limited-overs cricket no distinction is made between the two ways in which an innings is closed, using up all the overs or losing all ten wickets. In both cases the team have used up all the resources of their innings. In an uninterrupted innings, there is no difference between Team 1's score of 250, for instance, whether it were 250 for 3 wickets in 50 overs or whether it were 250 all out in 47 overs. Similarly in an interrupted innings, the method of target revision cannot and should not distinguish between whether Team 1's innings were terminated by being all out or by using up their allocation of overs.
4. When Team 2 have more resources than Team 1, why do you not simply scale up the target by the ratio of resources?
In the Professional Edition, which is now used in most top-level matches including ODIs, the problem of early high scoring rates producing anomalously high targets has been overcome, and so direct scaling is employed. So this question only relates to the Standard Edition.
In the Standard Edition, to scale up a target by the ratio of resources could lead to some unrealistically high targets if Team 1 had achieved an early high rate of scoring and rain caused a drastic reduction in the overs for the match; see Q10, for instance). We have preferred, therefore, to assume average performance for Team 1's additional loss of resource over Team 2.
5. But why should the target score sometimes go down if there is an interruption in the first innings and teams have the same number of overs?
In interruptions to the first innings the D/L method makes appropriate allowance for the comparative resources lost by the stoppage.
Consider the following situation. Suppose Team 1 started well in the style of the renowned Sri Lankan 1996 World Cup winning team but the wheels fell off and they were 150/9 in 30 of the 50 overs. On average Team 1 would be all out shortly, leaving Team 2 to score at the rate of around 3 per over for their full 50 overs. If rain interrupted play at this point and 19 overs were lost per side, then on the resumption Team 1 would have only one over to survive and their run rate would then be close to 5 per over. By all the 'old' methods, for 31 overs also, Team 2 would have to score around 150, around 5 per over, to win - in other words Team 1 would have been greatly advantaged by the rain interruption changing a required scoring rate of 3 per over to 5 per over for Team 2. By the D/L method this advantage to Team 1 would be neutralised so that the target for Team 2 would be well below 150 in this circumstance, and fairly so, which maintains the advantage Team 2 had earned before the stoppage. In other words, and quite logically, Team 2 have to get fewer runs than Team 1 scored to win in the same number of overs.
6. When Team 2 have the more resource, you increase the target by applying the excess resource to the quantity known as G50, which is the average score for a 50-over innings. Why do you not use a different value of G50 according to ground conditions on the day?
The quantity G50 is not used in the Professional Edition as used from the start of 2004, enhanced targets being calculated by scaling Team 1’s score in the direct ratio of the resources available to Team 2 and Team 1, so this question only applies to the Standard Edition.
The key is simplicity. We accept that the value of G50, perhaps, should be different for each country, or even for each ground, and there is no reason why any cricket authority may not choose the value it believes to be the most appropriate. In fact it would be possible for the two captains to agree a value of G50 before the start of each match, taking account of all relevant factors.
However, we not believe that something that is only invoked if rain interferes with the game should impose itself on every game in this way. In any case, it should be realised that the value of G50 usually has very little effect on the revised target. If 250 were used, for instance, instead of 235, it is unlikely that the target would be more than two or three runs different.
In the Professional Edition, the option has been retained for an average 50-over score to be input for the purposes of predicting Team 1’s eventual score from any point of their innings. This facility is purely for media or spectator interest and is not a part of the target calculation. Rather than use the default value of G50, commentators have the option of entering a ‘best guess score’ for 50 overs before the match starts, this taking account of ground conditions.
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