Around 2012, I started to see some sudden changes in the big national surveys – depressive symptoms and loneliness started to go up, and (after going up for 20 years) happiness started to go down. Other sources – like national screening studies on depression and statistics on teen suicides – showed the same pattern, with increases after 2010-12. I wondered what was going on, so I thought about what might possibly have caused these shifts. The Great Recession was officially over by 2010, and unemployment started to fall around 2011, so it seemed unlikely that the economy was to blame. This period didn’t see any cataclysmic events – and certainly none that kept accelerating over the next five years.

Then three things happened, and the puzzle pieces began to fall into place. First, the Pew Center’s data showed that the percentage of Americans owning a smartphone crossed 50% at the end of 2012. Second, I found that social media moved from optional to mandatory among teens in 2010 . Third, I and many others found that young people who spent more time on social media were less happy and more depressed. So this was a suspicious pattern: A sudden rise in mental health issues when smartphones and social media became ubiquitous, and a link between social media use and mental health issues. For more on this, see the excerpt of iGen in The Atlantic. Overall, GenZ is a less confident, more uncertain, more anxious generation than Millennials were at the same age. That may at least partially be due to their adolescence spent on their smartphones.

Since iGen was published, more studies have documented troubling trends in teen and young adult mental health in the U.S. since 2010, including increases in self-harm behaviors , suicide attempts by poisoning, hospital admissions for suicidal thoughts and suicide attempts, and suicides. Many of these increases are more pronounced among girls. Similar increases appear in the U.K. and in Canada. Jon Haidt (author of The Coddling of the American Mind) and I have reviewed the evidence for increases in adolescent mental health issues in a Google doc.