Thursday, 26 December 2013
Determining the best cricket team of all time using the Google PageRank algorithm
My plan for each summer holiday is pretty simple. It involves BBQs, the ocean, and watching the cricket. This summer we are being treated to an Ashes series, that at the time of writing, Australia has already won convincingly. England were regarded as favourites for this series and Australia has performed well above expectations. But how good are these teams compared with teams of the past?
Satyam Mukherjee at Northwestern University has come up with a novel approach to ranking cricket teams. In his paper, Identifying the greatest team and captain—A complex network approach to cricket matches, Mukherjee uses the Google PageRank algorithm to rank the various Test (and One Day International) playing countries, and also the team captains. PageRank works by counting the number and quality of links to a page to determine how important the website is. The underlying assumption is that more important websites receive more links from other websites. What Mukherjee has essentially done is instead of tracking links, he has tracked team wins, so that an estimate of a team's quality is made by looking at the quality of teams it has defeated.
After considering all Test matches played since 1877, and all One Day International matches since 1971, Mukherjee identified Australia as the best team historically in both forms of cricket, Steve Waugh as the best captain in Tests, and Ricky Ponting in ODIs. With regards to captains, it is hard to conclusively prove that it was the captain's influence that made them good teams - Australia under Waugh and Ponting were formidable and pretty much anyone could have captained them. This ranking method also only compares teams against their contemporaries. That is, it is not saying that Waugh's team was better than, say, Bradman's 1948 team. It is saying that Waugh's team was further ahead of the rest of the world than Bradman's was in 1948. Unless you have a time machine, it is very difficult to compare across era.
You can read more about how the Google PageRank algorithm works in The amazing librarian, and check out our previous article on sporting ranking systems for chess and sumo wrestling.
This is of course not the first study to apply objective science to a subjective topic within cricket. In the paper The effect of atmospheric conditions on the swing of a cricket ball, researchers from Sheffield Hallam University and the University of Auckland debunk the commonly held belief that humid conditions help swing bowling. But they don't discount the theory that cloud cover helps.
They used 3D laser scanners in an atmospheric chamber to measure the effect of humidity on the swing of a ball, and found that there was no link between humidity and swing. They postulate at the end of the paper that cloud cover may have an influence on swing. Cloud cover reduces turbulence in the air caused by heating from the Sun and they theorise that still conditions are the perfect environment for swing. When a ball moves through the air, it produces small regions of slightly higher and lower pressure at various points around it. This causes the ball to swing. If the air is already turbulent, it is more difficult to sustain these regions and so therefore there is less swing. Imagine throwing a stone into a still lake - the ripples around where the stone lands are easy to spot and move for some distance. Compare this to throwing a stone into an already turbulent ocean - you can barely spot the ripples as the turbulence in the water is much greater than any effects from throwing the stone.
If you think about the places where swing bowling has been most effective - England, New Zealand, Hobart - this theory appears sound, however more study is needed to prove it. So I'll endeavour to watch as much cricket as I can this summer, in the name of science.
Satyam Mukherjee (2012). Identifying the greatest team and captain—A complex network approach to cricket matches Physica A: Statistical Mechanics and its Applications DOI: 10.1016/j.physa.2012.06.052
David James (2012). The effect of atmospheric conditions on the swing of a cricket ball Procedia Engineering DOI: 10.1016/j.proeng.2012.04.033