The research investigated monotonic and non-monotonic temporal patterns in adolescents' psychological and somatic symptoms, including variations by gender. Analyses were conducted on repeated cross-sectional data from the Health Behaviour in School-aged Children (HBSC) survey spanning 1994–2022, involving 15-year-old adolescents from 41 nations (N = 470,797). Three polynomial logistic regression approaches (linear, quadratic, cubic) were evaluated for optimal fit, with stratified examinations by gender and symptom type.
Temporal patterns differed according to gender and symptom category. Rising trends appeared in 82.3% of instances (linear in 25%, U-shaped quadratic in 28.7%, cubic in 28.7%), whereas 14% lacked a distinct pattern, and 3.7% declined. Males predominantly exhibited linear rises or stable patterns, while females more commonly displayed cubic or U-shaped trajectories. Psychological symptoms frequently followed U-shaped or cubic trajectories, in contrast to somatic symptoms, which primarily demonstrated linear rises.Across nations, adolescents' psychological and somatic symptoms exhibited varied temporal trajectories, with non-monotonic forms (U-shaped and cubic) commonly occurring beside linear rises. Such results underscore the intricate nature of national-level shifts across three decades, indicating that sole reliance on linear models may inadequately represent this variability.
