Researchers like Twitter because almost all tweets are open, and the company provides an easy way to download the data, says Northeastern University computer scientist Alan Mislove, who worked on a study measuring “the pulse of the nation” published in 2010.

“You can get a large sample of data that covers a whole country or several countries,” he said. “You can get the text to look at sentiment, to look at patterns. This kind of data is being used by researchers in psychology, sociology, political science, geography.”