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How Significant Is Being on the Cusp of a Milestone Birthday?

Everyone seems to dread certain birthdays. Turning 30, 40 or 50 seems to have a bundle of negative connotations connected to these milestone events. No one wants to be “over the hill,” after all. But the findings of 2015 research conducted by marketing psychologists Adam Alter and Hal Hershfield point to a different dynamic facing people as they age. Using the term “nine-ender,” they studied “meaning-seeking behaviors” that seem to occur at ages ending in nine, such as 29, 39 and 49. They found that people tend to do extreme and/or ambitious things -- both good and self-destructive -- more frequently at ages ending in 9 than at other ages.

Number nine:

  • The research found that suicide rates among nine-enders were significantly higher than at other ages. They also chronicled more self-destructive acts, such as visiting online sites offering illicit relationships, more frequently.
  • They found that 29-year-olds were twice as likely to run marathons (compared to 28- or 30-year-olds), and 49-year-olds were three times more likely to attempt these grueling runs than people just one year older.
  • “These milestone birthdays end up disproportionately affecting us, making us take stock of our lives,” Hershfield says. “When we do that, we’re more vulnerable to seeking out meaning in a variety of ways.”
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