That doesn’t mean one should play the market based on search terms alone, however. The researchers observed a trend, but not all words fit the pattern. And if a lot of people were to find out that search terms can be linked to market movements (say by reading Scientific Reports), that signal could become useless or even be manipulated, says Preis.

But the fact that evidence for human decision making can be distilled from an enormous, preexisting data set rather than by conducting surveys or questionnaires is fascinating, says Alessandro Vespignani of Northeastern University in Boston. He and his colleagues are eager to find techniques that use digital traces left by people to predict human behavior. “It’s the meteorology of society,” he says.