James Surowiecki in "The Wisdom of crowds" about the scientist Francis Galton and collective Intelligence:As he walked through the exhibition that day, Galton came across a weight-judging competition. A fat ox had been selected and placed on display, and members of a gathering crowd were lining up to place wagers on the weight of the ox. (Or rather they were placing wagers on what the weight of the ox woiud be after it had been slaughtered and dressed.) For sixpence you could buy a stamped and numbered ticket where you filled in your name your address and your estimate. The best guesses would recieve prizes.
Eight hundred people tried their luck. They were a diverse lot. Many of hem were buchers and farmers, who were presumably expert at judging the weight of a livestock, but the were also quite a few people who had, as it were, no insider knowledge of cattle....
...Galton undoubtedly thought that the average guess of the group would be way off the mark. After all, mix a fex smart people with some mediocre poeple and a lot of dumb people, and it seems likely you'd end up with a dumb answer. But Galton was wrong. The crowd had guessed that the ox (after calculating the Median of all estimates), after it had been slaughtered and dressed, would weigh 1.197 pounds. After it had been slaughtered and dressed it weigthed 1198 pounds. In other words the crowd's judgement was essentially perfect.
Since then collective Intelligence is approved by the sciences as a "wisdom of crowds".
Recommendation of literature::
On its Odysso science program, regional public broadcaster SWR put the rule to the test in a video clip. View the experiment. ARD video (in german language)