Clearly, researchers love Facebook, even if some of the rest of us are ambivalent.

A 2012 survey of social science papers related to the social network turned up 412 separate studies, and there have been even more since. Among the most popular questions: What effect does Facebook have on emotional states?

It does seem a reasonable question. After all, about 22 percent of the world's population uses Facebook regularly, according to the company, logging on for about 50 minutes a day. But is all this interconnectedness creating psychological benefits or global gloom?

The answer, it turns out, is complicated.

Ethan Kross, the director of the Emotion & Self Control Lab at the University of Michigan, who has co-authored several papers about Facebook, says the early research was "all over the place" as to whether using the site boosted or depressed a person's mental state.

But it's the research finding a correlation between Facebook and feeling lousy that has drawn the attention of the media. A study making headlines in the spring looked at the relationship between social media use and depression. University of Pittsburgh researchers surveyed 1,787 U.S. adults, ages 19 through 32, and found three times the incidence of depression among the most active users of sites like Facebook, Twitter and Reddit than among those who used them the least.

Still, that doesn't mean use of the site is causing depression, the University of Pittsburgh researchers acknowledge. "It may be that people who already are depressed are turning to social media to fill a void," their study concludes.

Read the full article "Facebook And Mortality: Why Your Incessant Joy Gives Me The Blues" at  NPR.