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Grandma was right, putting a smile on your dial does make you happy.

And now, the scientists have worked it out, too.

Researchers at the University of Tennessee, Knoxville and Texas A&M in the US have examined nearly a half-century of data that tested whether facial expressions can make people feel the emotions related to those expressions.

“Conventional wisdom tells us that we can feel a little happier if we simply smile. Or that we can get ourselves in a more serious mood if we scowl,” said Nicholas Coles, a PhD student in social psychology and lead researcher on the paper.

“Psychologists have actually disagreed about this idea for over 100 years.”

In 2016, 17 teams of researchers failed to replicate an experiment that demonstrated that the physical act of smiling can make people feel happier.

“Some studies have not found evidence that facial expressions can influence emotional feelings,” Coles said. “But we can’t focus on the results of any one study. Psychologists have been testing this idea since the early 1970s, so we wanted to look at all the evidence.”

Cole and his team used a statistical technique called meta-analysis where they combined and examined data from 138 studies that involved more than 11000 participants from around the world.

What they found was that facial expressions have a small impact on feelings. They found that smiling makes people feel happier, scowling makes them feel angrier, and frowning makes them feel sadder.

Their findings were published in Psychological Bulletin.

“We don’t think that people can smile their way to happiness,” Coles said. “But these findings are exciting because they provide a clue about how the mind and the body interact to shape our conscious experience of emotion.

“We still have a lot to learn about these facial feedback effects, but this meta-analysis put us a little closer to understanding how emotions work.”