In 1906, the great statistician Francis Galton observed a competition to guess the weight of an ox at a country fair. Eight hundred people entered. Galton, being the kind of man he was, ran statistical tests on the numbers. He discovered that the average guess (1,197lb) was extremely close to the actual weight (1,198lb) of the ox. This story was told by James Surowiecki, in his entertaining book The Wisdom of Crowds.

Not many people know the events that followed. A few years later, the scales seemed to become less and less reliable. Repairs were expensive; but the fair organiser had a brilliant idea. Since attendees were so good at guessing the weight of an ox, it was unnecessary to repair the scales. The organiser would simply ask everyone to guess the weight, and take the average of their estimates.

A new problem emerged, however. Once weight-guessing competitions became the rage, some participants tried to cheat. They even sought privileged information from the farmer who had bred the ox. It was feared that if some people had an edge, others would be reluctant to enter the weight-guessing competition. With only a few entrants, you could not rely on the wisdom of the crowd. The process of weight discovery would be damaged.