A new study suggests teens whose eyes are habitually glued to their smartphones are markedly unhappier, according to  lead author and San Diego State University professor of psychology Dr. Jean M. Twenge.

Twenge, along with colleagues Gabrielle Martin at SDSU and W. Keith Campbell at the University of Georgia, analyzed data from the Monitoring the Future (MtF) longitudinal study, a nationally representative survey of more than a million U.S. 8th-, 10th-, and 12th-graders.