America depends upon the wisdom of crowds. When voting, we rely on the masses to pick the best politicians. When investing in stocks, we assume that, over time, people will gravitate toward the best companies. Even our culture is increasingly driven by the collective: Just look at "American Idol."

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...