The notion that a group’s judgement can be surprisingly good was most compellingly justified in James Surowiecki’s 2005 book The Wisdom of Crowds, and is generally traced back to an observation by Charles Darwin’s cousin Francis Galton in 1907. Galton pointed out that the average of all the entries in a ‘guess the weight of the ox’ competition at a country fair was amazingly accurate – beating not only most of the individual guesses but also those of alleged cattle experts. This is the essence of the wisdom of crowds: their average judgement converges on the right solution.
Still, Surowiecki also pointed out that the crowd is far from infallible. He explained that one requirement for a good crowd judgement is that people’s decisions are independent of one another. If everyone let themselves be influenced by each other’s guesses, there’s more chance that the guesses will drift towards a misplaced bias. This undermining effect of social influence was demonstrated in 2011 by a team at the Swiss Federal Institute of Technology (ETH) in Zurich. They asked groups of participants to estimate certain quantities in geography or crime, about which none of them could be expected to have perfect knowledge but all could hazard a guess – the length of the Swiss-Italian border, for example, or the annual number of murders in Switzerland. The participants were offered modest financial rewards for good group guesses, to make sure they took the challenge seriously.
The researchers found that, as the amount of information participants were given about each others guesses increased, the range of their guesses got narrower, and the centre of this range could drift further from the true value. In other words, the groups were tending towards a consensus, to the detriment of accuracy.
Full article here http://www.bbc.com/future/story/20140708-when-crowd-wisdom-goes-wrong