Between 2010 and 2015 Twenge found the number of teens who answered "yes" to three or more of these questions increased significantly, from 16 percent in 2010 to 22 percent in 2015.
By far the biggest increase was among girls — who were six times more likely than boys to report these or other symptoms of depression.
Twenge says the gender difference in the findings might be because the screen experience for boys — typically playing computer games — is a lot different than it is for girls.
"For girls, she says, "a lot of social media revolves around concerns about popularity — am I going to get likes on this photograph, do I look good enough in this picture?
The study also looked at survey responses to questions about suicidal thoughts.
"These include things like depression, thinking about suicide, making a plan to commit suicide and then actually having attempted suicide at some point in the past," Twenge says.
Her team found an increase in suicidal thoughts over that time period and,according to statistics from the Centers for Disease Control and Prevention, an increase in suicide deaths among teens from 1,386 in 2010 to 1,769 in 2015.
Again, the finding about suicidal thoughts was strongest among girls.
Financial stresses and anxiety related to academics and homework are often cited as factors in teen depression. But the overall economy improved between 2010 and 2015, Twenge notes. And surveys suggest the amount of homework given over that time period did not increase.
What did increase significantly, she says, was students' online activity, via computer games and social media.
Her research found that teens who spent the most time on their electronic devices were more likely to also show signs of depression.
Meanwhile, she says, the surveys suggested that hours spent in face-to-face activities — sports, parties, even just going to the mall with friends — seemed to be protective.
Nonetheless, psychologist Andrew Przybylski, an experimental psychologist at the University of Oxford in Oxford, England, takes issue with the researchers' conclusion that online activity is likely behind a shift in teen mood. Przybylski says teens may now simply be more willing to admit they are worried or sad.
"It could be that young people are reaching out, telling parents, telling friends," he says, "and certainly not feeling bad about filling out a survey about how they feel."
And the study doesn't eliminate the possibility that financial strains at home may have contributed to any genuine uptick in depressive symptoms among teens, says Przybylski. Even though statistics suggest the overall U.S. economy improved during the time period of the study, the researchers didn't explore what was happening in individual households in terms of job loss, for example.
Changes in a family's economic circumstances, he says, can be a leading cause of a child's depression.
Twenge responds that though her findings don't prove cause and effect, they are in synch with results from other studies, including some randomized trials — that have found that when people spend less time on electronic devices they tend to be happier and less lonely.
Twenge says the findings should spur continued research and, in the meantime, should serve as a warning for parents that if their teen spends lots of time online they may be at heightened risk of depression.
While the strength of the findings may be controversial, many parents worry about their child's reliance on social media, says Adam Pletter, a child psychologist in private practice in Washington, D.C.
Every day, Pletter says, he sees struggles between kids and their parents. Adults are often way behind, he says, when it comes to technology their kids are fluently using.
"We are digital immigrants," Pletter says. "We did not grow up with internet and cell phones — at least most of us did not. So there's a real dilemma, in that we're in charge of safeguarding our kids and teaching our kids how to be savvy digital users, and we don't have all the skills. Many of us are afraid of the technology."
Pletter offers workshops in person — and online — aimed at helping parents figure out ways to reduce their children's reliance, and in some cases, addiction, to screen time.
Copyright 2017 NPR. To see more, visit http://www.npr.org/.