JUDY WOODRUFF: Now: how our increasingly wireless world is affecting our social behavior, especially among the generation that has grown up with smartphones.

William Brangham has that.

WILLIAM BRANGHAM: The promise of social media, as the name implies, is that it connects us to each other, helps up become more social.

But according to a recent story in The Atlantic magazine, an increasing body of evidence shows that, for many teenagers, greater use of social media means a far greater sense of isolation.

According to the piece, teenagers now spend less time in the company of their friends, they date less, have less sex, and get less sleep than earlier generations.

And with this growing isolation comes a rise in cyber-bullying, feelings of being left out, and higher rates of depression and suicide.

The piece is called, "Has the Smartphone Destroyed a Generation?" And its written by author and professor of psychology Jean Twenge.

She joins me now from San Diego.

WILLIAM BRANGHAM: Welcome to the NewsHour.

JEAN TWENGE, The Atlantic: Thank you.

WILLIAM BRANGHAM: So, briefly, would you just please lay out the case that you're making in this piece that smartphones and social media have had this very detrimental effect on a younger generation.

JEAN TWENGE: Well, I have done work on the generational differences for a long time.

And right around 2011, 2012, I started to see some negative signs in the data, more depression, more anxiety. The suicide rate was starting to go up again. And I have realized that these are some sudden big changes.

Very rare to see such sudden changes in this type of work. I realized 2012, according to the data, is the year when the majority of Americans had a smartphone. So, that made me wonder if that might have something to do with it.

So, I looked at the same big data sets of teenagers and found that those who spent more time online or social media or on electronic devices also were more likely to be depressed and anxious and have risk factors for suicide.

WILLIAM BRANGHAM: You write in the piece that rates of teen depression and suicide have skyrocketed since 2011.

What is the evidence that these things are caused by access or heavy use of these devices?

JEAN TWENGE: Well, that's always the question.

So, the research that I did was correlational, so, that there's a link between the two. So, proving causation, really, you need a different type of method. But, fortunately, there have been other researchers who have used those types of methods.

There's two studies that have looked at adults over time and seeing that, when they use social media more, then their psychological well-being goes down and mental health problems increase.

There was another study called The Facebook Experiment, where people, by a flip of the coin, either continued their normal Facebook use or they gave up Facebook for a week. And those who gave up Facebook for a week at the end of the week were less lonely, less depressed and happier.

So those studies really point very strongly in that direction that the causal arrow moves from social media and screen time to lowered psychological well-being.

WILLIAM BRANGHAM: And you feel they confident that this effect could not be caused by other factors in society, the economy, employment, access to health care, so many other things that could drive our sense of well-being?

JEAN TWENGE: Yes, so I looked at the economy, because I wondered about that, too, because, of course, the great recession had a big effect on people. Unemployment really went up.

But if you look at the pattern for unemployment, for example, a good indicator of the strength of the economy, unemployment really peaked out at about 2010, and then went down, and is now quite low.

But the data for mental health goes in the other direction. It doesn't do a whole lot until about 2011 or 2012. Then it really shoots upward. So, unemployment doesn't seem to be the answer, at least economic factors.

And then other factors, it's hard to nail those down, but access to health care probably went the other direction as well at that time. It's difficult to identify any other big social change that happened around 2011 or 2012 that might be linked to mental health, other than smartphones.

WILLIAM BRANGHAM: What about this reaction that I have seen some people making online that this is just yet another generational freak-out, that this is like we did with violent video games or helicopter parenting or marijuana or rock ‘n' roll, that we are just flipping out because we as an older generation don't appreciate what this technology really is?

JEAN TWENGE: Yes.

Well, as a generations researcher, I have of course heard this argument before: Oh, it's just old people complaining about the young generation. Doesn't that always happen?

I have always found that argument confusing, because I don't care what older people say. I'm more interested in what young people say now compared to what young people said 10 or 20 years ago, so comparing the generations at the same age and really listening to young people and what they're experiencing and what they're feeling.

So I'm not really sure that argument is relevant.

WILLIAM BRANGHAM: Some of the things that you do cite, driving less, drinking less, not getting killed as often in cars, not getting as pregnant as often, those don't sound like necessarily terribly bad things to me as a parent.

JEAN TWENGE: Yes. They're not.

So this trend is going up slowly, the things you mentioned about driving, also working less, less likely to have sex and get pregnant as teenagers, less likely to drive. These are tradeoffs. So, 18-year-olds now look more look like 15-year-olds did just five to 10 years ago.

So, teens are growing up more slowly. The activities that adults do and children don't, they're just less likely to do those things. Some of those, people might identify as being a really good trend, like fewer teenagers having sex and getting pregnant.

Others are, I don't know, either one. Driving less, working less, it's not really a matter of, is this good or is this bad? It's that all of these trends come together with them growing up more slowly, taking longer to take on the roles, both the responsibilities and the pleasures, of adulthood.

WILLIAM BRANGHAM: Your piece also says that some of the more negative effects fall harder on girls than on boys. And I'm curious why you think that is.

JEAN TWENGE: Yes, so a lot of the mental health trends are more acute for girls than boys.

The increases have been much larger for girls than for boys. And my best guess is, that's because girls spend more time with their smartphones and more time on social media, and their interactions on social media are often more negative. So that might be one of the reasons why that mental health trend is more negative for girls.

WILLIAM BRANGHAM: Last question. If you were advising a parent who is trying to figure out a good mix of allowing their child to have this technology, but try to moderate it in some way, what kind of advice would you give them?

JEAN TWENGE: Well, I think, first, put off getting teen a smartphone as long as you can.

Sixth grade is really common now, even fourth grade. I have a fourth grader becoming a fifth grader. She said half of the kids in her class have a phone. The mental health effects are stronger for the younger kids. So, put that off.

And if you feel like they need it for taking the bus, get them a flip phone. Once they have that smartphone, there are apps where you can regulate how many hours a day they use that phone and if they're using it at night, because we want them to get a good night's sleep.

And we found that an hour, even an hour-and-a-half a day of use doesn't seem to have any negative mental health effects, but two hours and beyond, that's where we start to see the effects. And most teens are on their phones a lot more than two hours a day.

WILLIAM BRANGHAM: All right, Jean Twenge, a really, really provocative piece in The Atlantic magazine.

Thank you so much for being here.

JEAN TWENGE: Thank you.