(Illustration by iStock/smartboy10)
Like many parents, Panle Jia Barwick has worried about the effects of screen time on her children. A professor of economics at the University of Wisconsin Madison, Barwick wondered whether hard evidence backed her belief that excessive device time was harmful. She had worked with mobile-phone data in previous research, and so she saw an opportunity to find answers.
Barwick teamed up with Siyu Chen, an associate professor of economics in Jinan University in Guangzhou, China; Chao Fu, a colleague and professor of economics at the University of Wisconsin Madison; and Teng Li, a professor of economics at the International School of Business and Finance at Sun Yat-sen University in Guangzhou, China, to study the effects of youth mobile-device use. Chen had been working with university data for nearly a decade and immediately saw the potential of bringing that data into the project.
The researchers merged two data sources: mobile-phone data from carriers in China and university records. From GPS data generated by Chinese telecom companies, they traced the mobile usage by students, whose identities were anonymized and de-identified, and whose data were securely stored offline. They found direct evidence that screen time, largely spent on games, was crowding out study hours and sleep. Universities in China, in fact, had been collecting such data in an effort to tackle skyrocketing mobile-phone use among their students.
“Most students were playing on their phones in class and rarely listening to professors, which is why the universities commissioned a study with a telecom company,” Barwick says.
The researchers then wrote code to analyze two streams of language. First, university records detailed student course selections, grades, dorm assignments, post-graduate study, and for students seeking jobs, initial placement and first-year salary. Second, telecommunications data going back to 2018 allowed the researchers to track students across their university careers. Mobile phone records captured monthly app usage and geolocation codes every 10 minutes, enabling the researchers to follow anonymized and de-identified students from their dorms to classrooms.
Then a viral blockbuster game, Genshin Impact (“Yuanshen” in Chinese), launched during the sample period—attracting 100 million active users in its first year—offering a natural point of analysis. “Forty percent of our sample actively played this game,” Barwick says. “We saw very clearly how after the game was launched, many more students went to class late, left early, were more likely to be absent from class, spent less time in study rooms, and spent more time in the dorm playing the game.”
Their experiment found that higher app usage was associated with lower student GPAs, while health—measured by grades in physical education, a course required across China—also declined. They identified a contagion effect as well: Students randomly assigned to dormmates who were heavy app users before college were themselves more likely to become heavy users. After graduation, salaries fell. The researchers estimate an average decline of about 1 percent, a seemingly large figure because it reflects an average across all students, they note in the study. Other research suggests that this is roughly equivalent to the wage premium associated with one year of education.
“In terms of the effect, we can only point to correlation,” Barwick says. “So we had to use some instruments, such as the launching of the large blockbuster game. We also used another instrument: In 2019, China implemented a game-restriction policy for kids under 18 that indirectly affected students in our sample because many of them have friends who are under age 18.”
The Chinese government, increasingly concerned about the academic effects of social-app use, introduced time limits in 2019 and tightened the policy in 2021 to three hours per week for minors. Using this policy to segment their data, the researchers found that when students’ friends reduced their gaming, they also spent fewer hours playing games.
“This innovative research uses a unique dataset to tell us about an important social issue,” says Hongbin Li, a professor of economics at Stanford University. As of late 2025, 35 US states have introduced laws or policies restricting student cellphone use during school hours. College students, however, are only subject to rules set by the institution or individual faculty and instructors.
Find the study: “Digital Distractions with Peer Influence: The Impact of Mobile App Usage on Academic and Labor Market Outcomes” by Panle Jia Barwick, Siyu Chen, Chao Fu, and Teng Li, Quarterly Journal of Economics, forthcoming (NBER Working Paper No. w33054).
Read more stories by Daniela Blei.