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PHILADELPHIA (CBS) – Do you remember how old you were when you discovered the truth about Santa Claus? A new survey finds the average age when children stop believing in Santa is 8.

Psychologist Professor Chris Boyle, from the University of Exeter, surveyed 1,200 adults from around the world asking when they realized the truth about Santa and if learning the truth affected how much they trusted their parents.

The survey found 65 percent of people played along with the Santa myth as children even though they knew it wasn’t true.

Fifteen percent of people felt betrayed by their parents and 10 percent were angry when they found out Santa wasn’t real.

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“It has been fascinating to hear why they started to believe he is fictional,” said Professor Boyle. “The main cause is either the accidental or deliberate actions of parents, but some children started to piece together the truth themselves as they became older.”

While some children found out accidentally, others set traps to find out the truth.

Professor Boyle says one survey explained how a nine-year-old wrote a secret letter to Lapland, which wasn’t given to their parents, nothing from that list arrived from Santa on Christmas morning.

Other children also realized reindeer couldn’t fly and Santa would get hurt coming down a chimney when a fire was lit.

The study also found threatening a child about being on Santa’s “Naughty List” didn’t always work.