Importance: Smartphones are a pervasive feature of adolescents' daily lives, raising concern about how smartphones are used in contexts such as school that require sustained attention and self-regulation.
Objectives: To describe youths' smartphone use during each hour of the school day and examine whether smartphone use during school is associated with poorer cognitive control, a key developmental process underlying academic success.
Design, setting, and participants: This cross-sectional study of youths aged 11 to 18 years from the Southeastern US objectively assessed smartphone use every hour for 14 consecutive days between April 8, 2021, and February 2, 2022 (cohort 1), and February 1, 2023, and December 11, 2024 (cohort 2), providing thousands of data points to capture actual engagement.
Main outcomes and measures: The iPhone iOS (Apple) screen time report captured smartphone use at every hour. Cognitive control was measured in the older cohort using a go/no-go task, with the signal detection metric d' quantifying inhibitory control.
Results: A total of 79 participants (mean [SD] age, 15.10 [2.04] years; 41 [51.9%] female) participated in the study. Youths were using their smartphones during every hour of the school day, spending a total of 2.22 hours of the school day on their smartphones. Youths aged 15 to 18 years spent more time on their smartphones during school hours than those aged 11 to 14 years (mean [SD], 23.28 [18.34] vs 11.57 [16.83] min/h; F1,76 = 28.82, P < .001, η2 = 0.28). Youths spent a mean (SD) of 40.14 (39.56) minutes on social media and 13.85 (25.22) minutes on entertainment apps during school hours. Youths checked their smartphones a mean (SD) of 64.46 (32.83) times during school hours. More frequent smartphone checking was associated with lower d' values (F1,28 = 4.8, P = .04, η2 = 0.15), indicating poorer cognitive control.
Conclusions and relevance: This cross-sectional study found that youths use smartphones approximately one-third of the school day; this use was associated with reduced cognitive control. These findings highlight the need for school-level policies and digital literacy programs that address not only overall screen time but also habitual smartphone-checking behaviors that fragment attention.
Importance: On average, females live longer than males. Research on sex differences in longevity has traditionally focused on higher mortality among males; however, the contribution of female reproductive cancers to survival gaps between females and males remains insufficiently quantified.
Objective: To assess the female-to-male survival gaps by estimating the contribution of age, birth cohort, and cause of death to sex differences in survival, with a particular emphasis on female reproductive cancers-breast and gynecological cancers-in long-term longevity disparities.
Design, setting, and participants: This cohort study used population-level mortality data from 20 countries with complete records from 1955 to 2020 from the Human Mortality and World Health Organization Mortality Databases. Data were analyzed from January 2023 to September 2025.
Exposure: Geographic location (Australia, Austria, Belgium, Canada, Denmark, Finland, France, Hungary, Ireland, Italy, Japan, the Netherlands, New Zealand, Norway, Portugal, Spain, Sweden, Switzerland, the UK, and the US).
Main outcome and measures: The primary outcome was the truncated cross-sectional average length of life (TCAL), which incorporates historical mortality information for all birth cohorts alive at a given time. For each country, the sex gap in survival-measured as the difference in TCAL between females and males-was calculated, decomposed, and presented graphically by birth cohort, age, and calendar year.
Results: The analysis encompassed 264.4 million deaths from all causes (119.1 million female [45.1%]; 145.2 million male [54.9%]), including 11.5 million deaths from female reproductive cancers. The sex gap in TCALs ranged from 8.31 (95% CI, 8.28-8.34) years in Hungary to 4.22 (95% CI, 4.20-4.25) years in the Netherlands. Across all countries, females had a survival advantage for major causes of death, except for neoplasms at reproductive ages. In most populations, females aged between 35 and 60 years experienced a consistent cross-cohort excess in cancer mortality compared with males, mainly due to breast cancer and, to a lesser extent, gynecological cancers. Eliminating female reproductive cancers would increase the survival of females and expand the sex gap in TCALs by an estimated mean of 0.77 (95% CI, 0.75-0.78) years, ranging from 0.96 (95% CI, 0.92-1.00) years in Ireland to 0.51 (95% CI, 0.50-0.52) years in Japan.
Conclusions and relevance: In this population-level cohort study of 20 low-mortality countries, females aged 35 to 60 years experienced disadvantage in cancer mortality compared with males-a consistent pattern observed across birth cohorts and over time. These findings underscore the ongoing need for action on the prevention, early detection, and treatment of early-onset female reproductive cancers.
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