There is a new common symptom of the flu, in addition to the usual aches, coughs, fevers, and sore throats. Turns out a lot of ailing Americans enter phrases like "flu symptoms" into Google and other search engines before they call the doctor. That simple act, multiplied across millions of keyboards in homes around the country, has given rise to a new early-warning system for fast-spreading flu outbreaks called Google Flu Trends.
"This seems like a really clever way of using data that is created unintentionally by the users of Google to see patterns in the world that would otherwise be invisible," said Thomas Malone, a professor at the MIT Sloan School of Management. "I think we are just scratching the surface of what's possible with collective intelligence."