The wisdom of statistically manipulated crowds

The wisdom of a crowd is often in the eye of the beholder, but most of us understand that, at its most basic level, "crowd wisdom" refers to a fairly simple phenomenon: when you ask a whole bunch of random people a question that can be answered with a number (eg, what's the population of Swaziland?) and then you add up all the answers and divide the sum by the number of people providing those answers - ie, calculate the average - you'll frequently get a close approximation of the actual answer. Indeed, it's often suggested, the crowd's average answer tends to me more accurate than an estimate from an actual expert. As the science writer Jonah Lehrer put it in a column in the Wall Street Journal on Saturday: The good news is that the wisdom of crowds exists. When groups of people are asked a difficult question - say, to estimate the number of marbles in a jar, or the murder rate of New York City - their mistakes tend to cancel each other out. As a result, the average answer is often surprisingly accurate. To back this up, Lehrer points to a new study by a group...