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.
I experienced an emotional flip-flop myself around Thanksgiving of 2008, when I first joined up. For a week or so, I marveled at Facebook's ability to connect me to people who had long ago faded into the remotest recesses of memory. But by Christmas, I was in the midst of a full-fledged metaphysical breakdown.
Those scrolls down memory lane were killing me. Better to have left that kid from third grade, who now likes to post videos of his weightlifting triumphs, as I last remembered him — a skinny punk hitting a double off the schoolyard fence.
It was the collapse of that natural partition between past and present that I found upsetting, and a few months in, after noting the male-pattern baldness of yet another long-lost pal, I figured out why: Facebook punctured the intransigently juvenile aspect of my personality that had refused to recognize the passage of time.
And that, of course, provided yet another piece of evidence for the harshest reality of life: We are all going to die.
Nearly an hour a day
OK, that was my Facebook freak-out — how about yours?
Ask around. Lots of folks will volunteer one resentment or another. Maybe they don't like the time they spend on Facebook. Or they don't like the way people communicate on Facebook. Or they just don't like Facebook. As Laurence Scott wrote in his recent book on digital life, The Four-Dimensional Human, "Everyone knows someone perpetually on the brink of quitting" the site.
Yet, whatever gripes people have, they aren't hurting business. The amount of time we spend on Facebook and Instagram beats out our dedication to all leisure activities save one, James B Stewart recently noted in the New York Times. (Still the king: watching TV.)
Given the expanding role Facebook plays in a reported 1.65 billion lives or more, it's not surprising the site has been laden with a surfeit of social and political significance, credited with contributing to everything from a rise in adultery to the toppling of autocratic regimes.
Facebook and mental health
But what about contributing to depression?
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.
A spokesperson for Facebook pointed me to a meta-analysis it collaborated on with two researchers, one who is a computational social psychologist now working on Facebook's data science team.
That analysis points out that most studies about Facebook and psychological well-being have been done using cross-sectional surveys — which means they derive data from research participants at a particular point in time, rather than looking longitudinally to see how someone's mood or mental health diagnosis shifts after heavy use of a social media site.
"You really can't draw any conclusions about what effects online communication in general or Facebook communication in particular has from cross-sectional data," said Carnegie Mellon University psychologist Robert Kraut, a co-author of the meta-analysis (he's consulted for Facebook but isn't on staff there).
A happiness deficit?
I asked Kraut about another study last year that caused a media stir; it came out of the Happiness Research Institute in Denmark (the happiest place on earth, apparently). The institute asked half of 1,095 people, most of whom were daily Facebook users, to abstain from using it for one week.
"People who had taken a break from Facebook felt happier and were less sad and lonely," an online presentation of the study said. Those on a Facebook "fast" also "reported a significantly higher level of satisfaction" and significantly less stress than those sentenced to remain on the site.
The study was limited — the behavioral change lasted only a week, and the work has yet to be published in a peer-reviewed journal. But Kraut thought it a "reasonable" approach for starting to get at the way we use Facebook, and how that might influence mood.
A small 2013 study also looked at whether Facebook use influences people's assessment of their own well-being over time. Researchers texted online surveys to 82 people every day for two weeks, asking them questions like "How do you feel right now?" Their answers were correlated with their use of Facebook.
The more people used Facebook the worse they subsequently felt, the paper reported. The researchers said "multiple types of evidence" showed there was no confounding of cause and effect in the study.
"Facebook use may constitute a unique form of social network interaction that predicts impoverished well-being," they wrote.
The big green 'E'
Some researchers have divided Facebook use into the categories of "active" and "passive." Active use includes those activities that facilitate direct communications, like commenting on posts or sending messages; passive use refers to the mere consumption of information — like scrolling through your news feed and glimpsing the lawn furniture your cousin just bought.
A handful of studies from different labs have now established links between passive Facebook use and envy or other negative mental states, said Kross, who has co-authored one such paper.
According to a 2013 research paper from Germany, for example, "upward social comparison and envy can be rampant" on Facebook and other social networks. The online environment promotes "narcissistic behavior," the researchers found, "with most users sharing only positive things about themselves." Among the 357 participants in the German studies, the researchers turned up a large number of what they called "envy-inducing incidents" — most frequently related to travel and leisure, social interactions and "happiness."
Furthermore, the researchers said, some Facebook users seem to engage in an "envy-coping plan" that involves "even greater self-promotion and impression management." And that can trigger what they called a "self-promotion-envy spiral."
A one-upmanship arms race.
Another couple of studies that Kross and his team published in 2015 managed to isolate envy as the culprit in bumming people out, as opposed to other characteristics like the number of "friends" a user has or self-esteem.
"Passive Facebook usage predicted envy, and envy predicted declines in affective well-being," the researchers concluded.
They included in the discussion section of their paper an anecdote from Randi Zuckerberg, the sister of Facebook founder Mark Zuckerberg. "I've had friends call me and say, 'Your life looks so amazing," Randi Zuckerberg told The New York Times in 2013. "And I tell them, 'I'm a marketer. I'm only posting the moments that are amazing.' "
'Do we have to see that?'
A friend of mine, who doesn't want to give her name (would you?) has been telling me for years that she gets genuinely depressed on Facebook, and it has everything to do with envy. She finds the serial posters particularly annoying.
"There's this woman I know and she is constantly posting, and she does some amazing things," my friend complained. "There's this jealous part of me, that's like, 'Do we have to see that?' Everyone seems like they're happy on Facebook."
Yes. After plodding through these studies, I felt the need to reassess my own Great Facebook Freakout of 2008. It wasn't hard to see that, just beneath the Proustian navel-gazing on time gone by, there was also a strong component of rivalry: If some of those losers from third grade had not exactly set the world on fire, they'd at least managed to get a few sparks going, while I still seemed to be gathering twigs for kindling.
Not that realizing that made me feel any better. But even if I'd done super-well in this status game, just the act of comparison might have been deflating. Contrary to some studies — and consistent with others (naturally) — research on Facebook and depression published in 2014 indicated "engaging in frequent social comparison of any kind may be deleterious to one's mental well-being."
The 'happy' studies
There are studies showing Facebook can enhance a sense of social connection. A 2007 study, for example, found that college students who were heavy Facebook users reported higher levels of "social capital," consisting of resources like emotional support and job opportunities that can arise from membership in a social network.
A 2012 study found that posting status updates decreased loneliness, even when those updates elicited no response. And a 2010 study recorded moment-by-moment physiological responses when using Facebook. The equipment logged indicators of pleasant emotion when users actively sought out information or directly communicated with their Facebook friends, but fewer such positive feelings when passively browsing.
Kraut and his team found the same sort of thing in a study published this week in the Journal of Computer-Mediated Communication. Receiving "likes" on something you post may offer a small boost in mood, but getting a positive comment on the post from someone important to you is likely to be much more satisfying, the researchers found.
It's up to you
Kraut, whose studies of the emotional effects of using the Internet go back to its early days, told me research generally shows that whether your Facebook experience will be good or bad depends on how you use it.
"In particular, having longer, more substantive communication with people you feel closer to seems to be associated with increases in psychological well-being," he said. "You don't get the same effects if the communication is with people who are weaker ties. What seems to be crucial is that these are effortful, targeted communications."
Kraut's advice: "Don't treat it as simple entertainment and consume everything that is put in front of you," he said. "Use it more proactively to communicate with people that you care about."
That sounds about right. Personally, I've made my peace with the site. It's true I sometimes find myself scanning that unceasing river of flattering photos, adorable babies and pronouncements of good fortune with a hollow sense of diminishment. Facebook offers a plethora of choices as to how I want to spend my time, and I don't always make the right one.
But in that, Facebook is a lot like life.
This story was produced by KQED's Future of You blog. Jon Brooks is a longtime KQED reporter and editor, and the blog's host.