WHO ARE DUCKWORTH AND LEWIS ??

I was really interested in writing this post , but i did not get a right event to describe the non understandable people Frank Duckworth and Tony Lewis . Yes these two were the kings who devised the D/L method , which not even a greatest cricket follower or king commentator say Tony Greig can understand .


It was a pity that Yesterday`s (28.9.09) match between India and Australia was abandoned due to thunder storms . I was following the text commentary in Cricinfo , where the calculations started for the D/L method , before the watch was officially called off . If India had to bat again given the conditions were good and rain stopped , India had to chase down 166 in 20 overs .

I was puzzled on looking at those numbers , this is what complexity can do to you ! Luckily it rained and the match was called off . So what is this D/ L method all about , i did a small search and found out these .

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 , 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.

The D/L method is relatively simple to apply, but requires a published reference table and some simple mathematical calculations. As with most non-trivial statistical derivations, however, the D/L method can produce results that are somewhat guessable, and the announcement of the derived target score can provoke a good deal of second-guessing and discussion amongst the crowd at the cricket ground. This can also be seen as one of the method's successes, adding interest to a "slow" rain-affected day of play.

Applied to 50 over matches, each team has to face at least 20 overs before D/L can decide the game. In twenty20 games, each side has to face at least 5 overs.

	Wickets lost
Overs left	0	2	5	7	9
50	100.0	83.8	49.5	26.5	7.6
40	90.3	77.6	48.3	26.4	7.6
30	77.1	68.2	45.7	26.2	7.6
25	68.7	61.8	43.4	25.9	7.6
20	58.9	54.0	40.0	25.2	7.6
10	34.1	32.5	27.5	20.6	7.5
5	18.4	17.9	16.4	14.0	7.0

Reading the table

The single table applies to all lengths of one-day matches from 50 overs-per-side downwards. Because this length of match is by far the most common, the resources listed in the table are expressed as percentages of those available at the start of a 50-over innings. Thus when there are 50 overs still to be received and no wickets have been lost, the resource percentage available is 100%. A 40-over innings starts with a resource percentage of 90.3% relative to a 50 over innings. An innings shortened to 25-overs before it starts commences with a resource percentage of 68.7% relative to 50-over innings. (Although such innings have only half the overs of a 50-over innings they have all 10 wickets and so have much more than half the resources.)

In order to determine the correct resource percentage the batting side has remaining at any stage of its innings, the number of overs left must be identified. This number of overs left, in conjunction with the number of wickets lost, is then used to read the resource percentage remaining from the table.

For example, suppose that after 20 out of 50 overs a team have lost 2 wickets. They have 30 overs left. From the table you will see that the resource percentage remaining is 68.2%.

Suppose now that there is an interruption in play and 10 overs are lost from the innings. When play can resume there are only 20 overs left but there are still, of course, 2 wickets down, and the table now tells us that the resource percentage remaining is 54.0%. Thus the shortening of the innings has caused the team to lose a resource percentage of 68.2 - 54.0 = 14.2%.

Having started with a resource percentage of 100% and lost 14.2%, then if they complete their innings with no further loss of overs, they will have had a resource percentage available for their innings of 100 - 14.2 = 85.8%.

My god , i did not think cricket was such a complicated game . Cricket still needs a better system to manage rain affected matches and in a way common man can understand that . Till that happens one can pray that rain does not play spoil sport !!