The suicide rate among teen girls reached a 40-year high in 2015, according to new analysis from the Centers of Disease Control and Prevention.

Researchers found a substantial increase in suicides among teen girls and boys in the U.S. from 1975 to 2015, with the rate among girls hitting a record high. From 2007 to 2015 alone, suicide rates doubled among teen girls and by more than 30 percent among teen boys.

While the suicide rate fell in 2007—3.7 to 2.4 per 100,000 girls and 18.1 to 10.8 per 100,000 boys—it spiked again in 2015 to 5.1 per 100,000 girls and 14.2 per 100,000 boys. To put it another way: In 2015, 5 girls per 100,000 committed suicide compared to 14 boys.

Overall, this analysis speaks to a rising national trend, CDC suicide expert Thomas Simon told CNN.

“We know that overall in the U.S., we’re seeing increases in suicide rates across all age groups,” he said, adding that the pattern is “pretty robust.”

It’s unlikely there’s any one factor to explain this increase, Simon said, but possible risk factors include a history of substance abuse, mental health stigma, and lingering economic stress from the Great Recession in the 2000s.

“In times of economic prosperity, suicide rates go down,” he said. “In times of economic instability, suicide rates go up.”

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