Digital Technology has caused the biggest changes to teenage life in many decades. Typical American teenagers spend about half of their waking hours on their smartphones. They are on the phones when they are alone at home and when they are hanging out with friends.

When I compare my own teenage years in the 1980s with those of my parents in the 1950s and '60s, I realize how much more rapidly habits have changed in the past 15 years than in the previous 50 years. My teenage experiences and those of my parents weren't all that different. We talked on the telephone, drove cars, watched movies, went to parties and so on. My children's social rhythms look much different.

This transformation has surely had broader consequences. To put it another way, if there have been major swings in teenage well-being over the past 15 years — good or bad — we should assume that the reshaping of life by digital technology has helped cause them.

Of course, there have been major swings in teenage well-being. By many measures, teen mental health has deteriorated, especially for girls, since about 2008. The suicide rate for girls and boys began rising around then. Feelings of loneliness and sadness began rising, too. The amount of time teenagers spend socializing in person has declined. So has sleep. "Young people are telling us that they are in crisis," Kathleen Ethier, a top C.D.C. official, said this month when releasing the results of a large survey.

Some other trends have been positive: Teenage deaths in vehicle accidents began falling more rapidly about 15 years ago. Teen pregnancies and bullying are down as well.

The release of the C.D.C. report has led to a raging debate among experts and journalists about whether technology deserves much blame (or credit) for these trends. My own takeaway is that while many uncertainties remain — and technology does have benefits — there is good reason to believe that technology use is the primary cause of the problem.

Even the positive trends in teen health point to technology: Pregnancies, vehicle deaths and bullying are down partly because teenagers are spending more time by themselves and less time together.

The counterarguments defending technology tend to have two big weaknesses. First, they exaggerate the significance of narrow academic studies. Second, nobody has come up with a persuasive alternative theory that fits the timeline of teenagers' struggles. I go into more detail on both points below.

Doomerism isn't new

My colleague Michelle Goldberg devoted her latest Opinion column to explaining why the timeline of the past two decades strongly suggests that technology has harmed mental health. The leading alternate explanation — call it the hellscape theory — argues that teenage misery is a rational response to Covid, Donald Trump, climate change, mass shootings, misogyny and other problems. But, as Michelle notes, the timeline doesn't fit.

The deterioration of teenage mental health predates Covid and Trump — and the deterioration is evident in countries that didn't elect Trump and don't endure mass shootings. The mental health trends line up better with the spread of digital technology, including the introduction of the iPhone (in 2007) and the rise of selfie culture (around 2012).

I'll add one point to Michelle's case. Earlier periods in American history also created grist for teenage angst. Schoolchildren in the 1950s feared nuclear annihilation. The 1960s included the Vietnam War, riots, assassinations and murders of civil rights activists. In the 1970s, popular culture was full of predictions that overpopulation would cause the world to run out of food.

None of this previous doomerism created a teenage mental health crisis like today's.

Carl Sagan's wisdom

As for the academic research, much of it does find that digital technology makes teenagers less happy.

One clever study used the variation in the times when Facebook arrived on college campuses and found that anxiety tended to rise after its introduction. Another paid people to quit Facebook and found that they felt better. By one count, 55 studies have found a correlation between social media use and mental health problems, compared with 11 that found little or none.

Skeptics point out that the magnitude of the effects is often modest. But that's to be expected. The studies are necessarily narrow because they don't eliminate digital technology from their subjects' lives. People who quit Facebook can still spend hours staring at their phones — experiencing FOMO or wondering why their friends aren't immediately replying to a message — rather than socializing face-to-face with other human beings.

Overemphasizing the small magnitude of findings from limited academic studies reminds me of a point that the astronomer Carl Sagan liked to make: Absence of evidence is not evidence of absence. Some questions don't lend themselves to an elegant experiment. Sometimes, the totality of the evidence is stronger than the average correlation across a group of artificial experiments. And people sometimes need to make real-world decisions before academic studies can offer unambiguous conclusions.

Practical advice

With this reality in mind, I called Lisa Damour last week and asked what advice she would give to parents. Damour is a psychologist who has written two best-selling books about girls and just published a new book, "The Emotional Lives of Teenagers." She is no anti-technology zealot. She thinks social media can have benefits for teenagers, including connections with peers. But she also sees reason for concern.

Her first piece of advice is not to blame teenagers. They didn't invent smartphones, and earlier generations would have used those phones in the same ways that today's teens are.

Her second piece of advice might be summarized as: less. She believes teenagers should rarely have their phones in their bedrooms, especially not at night. A phone is too disruptive to sleep, and sleep is too important to mental health.

Parents can also introduce digital technology in stages, recognizing that a 13-year-old brain is different from a 17-year-old brain. For younger teens, Damour suggests a phone that can send and receive texts but does not have social media apps.

I know that some people think it's impossible to deny Instagram or TikTok to a teenager. But it's not. If you talk to parents who have done so, you will often hear that it is quite possible — and that they have no regrets about having done so.

Related: A Times guide to helping teens who are struggling with mental health.

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Thanks for spending part of your morning with The Times. See you tomorrow. — David

P.S. Berlin's Reichstag building burned 90 years ago today.

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Matthew Cullen, Lauren Hard, Lauren Jackson, Claire Moses, Ian Prasad Philbrick, Tom Wright-Piersanti and Ashley Wu contributed to The Morning. You can reach the team at [email protected].

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