"Measuring how calm the Twitterverse is on a given day can foretell the direction of changes to the Dow Jones Industrial Average three days later with an accuracy of 86.7 percent. 'We were pretty astonished that this actually worked,' said computational social scientist Johan Bollen of Indiana University-Bloomington. The new results appear in a paper on the arXiv.org preprint server. Bollen and grad student Huina Mao stumbled on this computational crystal ball almost by accident. Earlier studies had found that blogs can be used to gauge public mood, and that tweets about movies can predict box office sales."