Sandy Strang: Impossible to calculate just how important D/L have been

Yet more monsoons. Yet more games cancelled or disrupted. And, yet again in this rain-ravaged Scottish summer, we've grounds to be grateful to the most celebrated double act in modern cricket, Frank Duckworth and Tony Lewis, authors of the Duckworth/Lewis method, aka D/L. Not even Hobbs and Sutcliffe were abbreviated to H/S.

It was back in the early 1990s that those two West Country statisticians devised a mathematical formulation to calculate the target score for the team batting second in a one-day - and more recently, and more contentiously, a T20 - cricket match interrupted by weather or other circumstances. No fewer than 23 SNCL matches so far this season have been resolved under its jurisdiction - not forgetting four of the five Scottish Cup Third Round ties concluded at the first time of asking.

Yet D/L remains an esoteric mystery to many inside and outside the game.

"I can't work it out", admits Aussie legend Steve Waugh, "but I think it's a good system. You're rightly awarded for taking wickets."

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, namely the number of overs they receive, and the number of wickets they have in hand. At any point in any innings a team's ability to score runs depends on the combination of these two resources. Historical analysis reveals a very close correspondence between the availability of these resources and a team's score, a correlation which D/L exploits.

Here in Scottish club cricket we deploy the Standard Edition, based on a single table and simple calculation. However since 2004 all ODIs have used the Professional Edition, which utilises substantially more sophisticated statistical modelling requiring the use of a computer.

The brilliance of D/L is that it translates an imponderable set of circumstances into the precise language of mathematics, and does so in a formula which can cope with an almost infinite number of variables - not least a series of rain interruptions requiring instant recalculations. Above all it maintains the integrity of the game.

The D/L method has been criticised on the grounds that wickets, necessarily, are a more heavily weighted resource than overs, leading to suggestions that, if teams are chasing big targets and there's the prospect of rain, a winning strategy could be merely not to lose wickets and score at what would superficially seem to be a "losing" rate. For example, if the asking rate was 6.2 runs per over, it could be enough to score at, say, 4.8 an over for the first 20-25 overs - each team being required to face at least 20 overs before a game can be validated and D/L applied - to win via D/L.Another complaint is that, while D/L is now well proven in 50-over matches, in its present form it is a less secure model for the more telescoped T20 format, too often presenting seemingly wonky targets.

In the 2010 T20 World Cup, for instance, Sri Lanka were very nearly eliminated because Zimbabwe were only deemed to need to score 44 in five overs in response to 173 for 7, while the West Indies defeated England with a mere 60 for 2 in six overs.

The famous D/L graph with its many curves which has gradually evolved through a number of improving incarnations has clearly some way to go to avoid presenting anomalous contractions in T20 but it's now firmly established for the staple 50-over diet, including our own SNCL.

If the prevailing weather of summer 2011 is extrapolated - beware, this mathematical jargon is catching - into the second half of the season then that most quoted partnership in Scottish cricket will continue to be those two marvellously prescient number crunchers, Duckworth and Lewis.