"Track displaced sleep and socializing to spot harm Jean Twenge noticed teen depression rising around 2012 and searched for a cause, finding that at the same turning point, teens were sleeping less and spending less time with friends in person. She realized these weren't separate mysteries: "We have depression going up. We have less time with friends in person, less time sleeping. What might possibly explain that?" Smartphone ownership passing 50% around that same moment tied it together. If you want to audit your own or your child's well-being, start by tracking hours of in-person socializing and sleep before looking at screen time — those displaced behaviors are the clearest early signals of harm. Source: Jean Twenge, The Happiness Lab, Social Media and Teen Mental Health"