Happiness is not a warm phone, according to a new study exploring the link between adolescent life satisfaction and screen time.

Teens whose eyes are habitually glued to their smartphones are markedly unhappier, said study lead author and San Diego State University and professor of psychology Jean M. Twenge.

To investigate this link, Twenge, along with colleagues Gabrielle Martin at SDSU and W. Keith Campbell at the University of Georgia, crunched 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.

The survey asked students questions about how often they spent time on their phones, tablets and computers, as well as questions about their in-the-flesh social interactions and their overall happiness.

On average, they found that teens who spent more time in front of screen devices--playing computer games, using social media, texting and video chatting--were less happy than those who invested more time in non-screen activities like sports, reading newspapers and magazines, and face-to-face social interaction.

"Although this study can't show causation, several other studies have shown that more social media use leads to unhappiness, but unhappiness does not lead to more social media use," said Twenge, author of "iGen: Why Today's Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy--And Completely Unprepared for Adulthood."

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