Is it possible to work out which living athlete is the best? Mathematician Rob Eastaway, co-author of The Hidden Mathematics of Sport, investigates.
The case for Indian batsman Sachin Tendulkar is certainly strong. His international career has spanned an astonishing 22 years, during which time he has never been dropped from the Indian Test side.
The "Little Master" has scored more runs and notched up more international hundreds than anyone else in the history of the game, although cricket fans will always be compelled by Donald Bradman's famous 99.94 batting average. And it's not just that he has scored more, it's the huge margin by which he tops the table.
Longevity and the accumulation of trophies is certainly an important factor in making greatness, but it is surely not the only one. After all, if you're only looking at durability at the top, then Tendulkar is outstripped by US golfer Tom Watson, who has been a serious challenger in the Open since 1975.
The trouble is, there are so many statistical ways to measure greatness.
One is to pick out those sportsmen and women who for a period of time are in a different class from their peers. The goal-scoring feats of Lionel Messi make him a candidate, but statistical measurements of footballers are always tricky, not least because it can be hard to disentangle one player's performance from the contributions of his team mates.
The feats within individual sports are easier to assess, and in terms of quantum leaps, can anyone rival Usain Bolt?
The 100 metre sprint is the pinnacle of athletics where the world records normally mean shaving 1/100th of a second off the previous best time. Yet Bolt has broken that record not just once but three times, and in his most recent, mathematicians reckoned he could have knocked more than a tenth of a second off the record time had he not slowed up at the finish because his shoelace was undone.
Great sportsmen are head and shoulders ahead of the competition. In Bolt's case it's head, shoulders and a couple of strides too.
Or you can take a look at a sport's world rankings. Every sport uses a different system for rankings its members, but all of them are based on some form of objective, mathematical model.
To identify the world's greatest, why not look at which sportsman has managed to spend the longest amount of time as world number one. Tiger Woods managed to be top of the golf rankings for over 10 years, before his recent fall from grace. By this measure, though, there's a British sportsman who pips Tiger for the title.
Phil "The Power" Taylor has had an almost unbroken position as world number one in darts since 1998. And yes, darts is now officially a sport.
We can of course let the market decide. If a sportsman earns a lot of money, it must reflect his global appeal and success.
David Beckham, surely a great, has earned tens of millions over his career.
Yet on this score, the world's greatest sportsmen at the moment could be Alex Rodriguez. He's paid around $30m (£18m) per year, and that's before all the product endorsements. He plays baseball.
But can he really be called the world's greatest when his name barely registers in public consciousness outside his own country?
Of course greatness also depends on many things that are hard to measure - charisma, style and an ability to hit the headlines, for example.
With all this complex and sometimes conflicting data, perhaps we should put our trust in the wisdom of crowds.
Despite the diverse and often ill-informed opinion of the public, put enough people together and they often manage to come up with the right answer.
And if we ask the crowd who is the greatest sportsman, I think I know who'll come out top. Sachin Tendulkar.
Why? He would win by sheer weight of population. There are over a billion people in India who have little sporting interest other than cricket. And a billion people can't be wrong - can they?