Jean Twenge had never seen anything like it. The San Diego State University professor in personality psychology had been studying generational differences for 25 years, since she was a 22-year-old Ph.D. student at the University of Michigan. Her research has generated more than 120 scientific publications. But in 2012, when the proportion of Americans who own smartphones surpassed 50 percent, she noticed abrupt changes in teen behavior and emotional states.
"In these big national surveys of teens that I keep an eye on, there started to be some pretty sudden changes in the ways teens use their time and how they said they were feeling in their mental health," she said. "And at first I thought maybe it could be a blip for a year or two, but it kept going."
Among other things, teens are: not hanging out as much with friends, in no rush to drive, dating less, having less sex, and getting less sleep. Most alarming, despite their continual connectivity, they are lonely. And rates of teen depression and suicide have skyrocketed since 2011.
"On these big surveys there are six questions that asked about loneliness, including, 'How often do you feel lonely?' and, 'How often do you feel left out?' And the responses show that same pattern of mental health not having done much, or even gotten a little bit better, until 2007," she said. "Then they start to tick up, and in 2012 those feelings of loneliness and feeling left out shoot upward. And that, of course, is maybe due to social media, where teens can see everything that their friends are doing that they didn't get invited to."
The result of Twenge's deep dive into multigenerational data of more than 11 million individuals, cutting across income, racial, and regional boundaries, is her new book: iGen: Why Today's Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy — and Completely Unprepared for Adulthood — and What That Means for the Rest of Us.
Twenge seeks to add to the current generational demarcations of boomers, genXers, and millennials with the iGen — those who were born between 1995 and 2012. What she calls the iGen have never known a world without smartphones. Yes, millennials were raised with internet access but not constant connectivity.
"I settled on '95 because those teens who are around 17 years old or so showed those sudden changes around 2012," she said. "Also, 1995 just happens to be the year the internet was commercialized. So iGen are the ones who have never known a world without the internet."
"The devices they hold in their hands have both extended their childhoods and isolated them from true human interaction," she writes.
[Read more: 5 questions: Is your child addicted to technology?]
The book is chock-full of information, often represented in graphs, that show a continuum of data points regarding teen emotional health and then a decline once we enter the age of the smartphone, beginning with the 2007 release of the iPhone.
"It's not an exaggeration to describe iGen as being on the brink of the worst mental-health crisis in decades," she told me. "Much of this deterioration can be traced to their phones. It's not just the technology, I should stress, it's really the social media, which is the most common risk they are facing."
According to her research, teens who spend more time than average on screen activities are more likely to be unhappy, and those who spend more time on nonscreen activities are more likely to be happy. And many of the problems are most pronounced among girls.
"I found that teens are spending less time with their friends in person," Twenge said. "They're not hanging out with their friends as much or going to movies or going to the mall or riding around in cars or going to parties as much as they did even 10 years ago. And that's probably because they're spending so much time communicating with their friends through their phones. And that is also another really key piece of why these mental-health issues have started to go up so steeply. It's not just that they're spending time with the screens, which isn't very fulfilling and probably has negative effects, but also not doing these in-person activities, which are beneficial."
So, what to do? The good news is there is no need to go cold turkey.
"Sporadic use is unlikely to be harmful," she said. "Electronic device use was linked to unhappiness and mental-health issues only after more than two hours of use a day."
Parents should consider installing apps that limit time spent on smartphones and that limit teens to one social-media site. Twenge, a mother of two iGen daughters, favors Snapchat.
"It's a really stressful thing where there's this constant social comparison — how everybody you know only puts the positive stuff on social media," she said. "The constant worrying about 'How many likes did I get on that?' And feeling anxious when you don't get enough likes, and then try to cultivate your life in your image so you can get more likes. It's really no wonder that there's more anxiety and depression when you think about it that way."
Perhaps most important, don't allow teens to sleep with access to the device.
My advice after being consumed with her book? That we all make the data contained in her book a point of discussion with our kids.
Michael Smerconish can be heard from 9 a.m. to noon on SiriusXM's POTUS Channel 124. He hosts "Smerconish" at 9 a.m. Saturdays on CNN. @smerconish