In 2011, three professors from Carnegie Mellon University conducted a series of studies to analyze the reason why some issues are more effective than others. In one experiment, they used the "think-out method", in which participants worked through the inbox of their mail and recounted their decisions about what they read, responded, forwarded or deleted. The researchers found that participants based their decisions on two factors: usefulness and curiosity. People predictably "read emails that directly affected their work." This is no surprise. But they were also likely to "open messages when there was a moderate level of uncertainty about the content, that is, they were" curious "about the content of the messages.