The Ashes: cricket ruled by Benford’s law


England celebrate in front of the 'barmy army' after retaining the Ashes for the first time in 24 years.

For those of you who don’t watch cricket, or even know what it is, it is often described to novices as an 11-a-side bat and ball game that lasts up to 5 days, sometimes ending in a draw.  For cricket followers, though, a 5 day test match is a chance to immerse yourself in the ebbs and flows of cricketing tension and to discuss endless batting and bowling statistics.

So, to the Ashes – the pre-eminent cricket series played between England and Australia and dating back to 1882.  We’re currently 4 tests into the 2010-11 series, England have won two tests, Australia one and one has been drawn.  This means that, even with one test to go,  England retain the Ashes for the first time in a generation.  In four test matches of two innings for each team, England have scored around 2,000 runs with batsmen getting anything from zero to a massive 235 runs (Alastair Cook in the Brisbane Test).

Now, cricket is an intensely strategic sport.  The decision of whether to bat or bowl after the toss of the coin on the first day can decide the whole series.  And that’s just the start of it: how do you deploy your fielders; when do you use your spinners or your seam bowlers; how will the state of the cracks in the pitch affect the bounce (I’ve supervised not one but two PhDs in this area)?

So, how surprised was I to find that all that has gone on in the Ashes down the years can be boiled down to one law – Benford’s Law, first postulated by Simon Newcomb just one year before the first Ashes series 130 years ago?

Figure 1. The occurence of leading digits according to Benford’s Law.

Sometimes called the ‘first digit phenomenon’ Benford’s Law (named after Frank Benford following his 1938 paper) can be applied to large lists of numbers such as cricket scores, the stock market, voting patterns and even the number of lightning strikes per day.  The law says that if we look at the first digit of each number in a list (not including zero), then the distribution of these digits will always be the same.  The digit ‘1’ will always lead 30.1% of the time, digit ‘2’ 17.6% of the time, digit ‘3’ 12.5% of the time and so on.  The distribution for 1 to 9 are shown in Figure 1.

Table 1. Englands 1st innings in the Brisbane Test Match.

Taking the example of The Ashes, consider the runs in England’s 1st innings at Brisbane in Table 1.   The digit 1 leads twice, 2 leads once, 4 twice, and 6 and 7 once.  If we do this for all innings and tests for England and Australia separately, then we can compare the 2010-11 Ashes scores with Benford’s law (Figure 2).

Figure 2. The occurence of the leading digit for batsmen’s scores in the 2010-11 Ashes series.

Given the human endeavour that goes into a cricket game (and indeed any sporting occasion), it is surprising that our efforts can be described by something as simple as the % occurence of the numbers 1 to 9.  Of course, there are some differences between the cricket scores and Benford’s law:  the digit 1 occurs more often than expected for England due to a lot of scores in the teens in the 3rd test; equally the digit 5 occurs more often than expected for Australia due to a larger number of scores in the 50s, particularly in the 2nd test.

Given the small sample of data we are using (n=46 for England; n=68 for Australia) there is probably not enough data to do a good comparison and we might consider that all this has occurred by chance.  Out of interest, I went back to the first Ashes series in 1882-3 to see if anything similar occurred (Figure 3);  again, the distribution follows Benford’s law pretty well apart from the preponderance of 2s for England due to a lot of scores in the 20s.

Figure 3. The occurence of the leading digit for batsmen’s scores in the first Ashes series in 1882-83.

To me, the whole thing is all a bit mind-blowing.  I spend a lot of time working on sophisticated projects to influence performance in sport, and yet here is a mathematical technique that seems to describe pretty simply a game as complex as cricket over a 130 year span.

So, how can we use it?  It could be used for almost anything number related; in cricket that could be runs per over, runs per batsman, overs per hour.  In other spheres, Benford’s law is used is to detect unusual behaviour, such as voting irregularities and stock market fraud.  Given the occasional accusations of cheating in cricket, perhaps we should use it for that?

 

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About stevehaake

Steve did a first degree in Physics at the University of Leeds before landing two job offers: the first with BT turned out to be in a porta-cabin in the middle of a marsh, while the second was supposed to be image processing but was really smart-bomb design. This left a third option – a PhD in the mechanics of golf ball impacts on golf greens for a person who’d never hit a golf ball. It was a simple choice (the PhD if you didn’t guess) which led 25 years later to being head of a research team of 30-40 looking into similarly unlikely topics. Highlights of the career so far? The early years setting up the ISEA with the likes of Steve Mather, Ron Thompson, Clive Grant and Ron Morgan; the fact that the 1st International Conference on Sports Engineering in Sheffield in 1996 didn’t also turn out to be the last; and getting out the first issue of the first journal on Sports Engineering in 1998. The absolute high point, though, was being in the British Club in Singapore as a guest of the High Commission when the bid for the 2012 Olympics was announced. This has led to the team delivering projects with Olympic athletes that every scientist with a love of sport can only dream of. Steve is now a Senior Media Fellow funded by the EPSRC to encourage the public to engage in science, particularly in the lead up to the London 2012 Olympic Games.

3 Responses

  1. Austin Yun

    It seems ridiculous to me that this would only hold in decimal. Am I correct to assume that the same thing occurs in other bases? Could it maybe be generalized to something like low numbers occur more frequently than high ones? (But rigorous and specific, of course). Is there a mathematical basis behind the specific values, or is it purely statistical?

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