**4. Discussion**

This paper furthers our understanding of the mean levels and trends in adolescents' report of LS over three time points, as well as the association between sex, age, time, stress domains, and LS in adolescents. Three findings stand out in this study: (a) the generally

stable level of LS across the three time points investigated, although significant differences in LS scores were found between 2011 and 2016; (b) the significant but modest role of demographic factors in association with LS; and (c) the significant negative association between stress domains and LS with interaction effects of sex by stress domains found.

Similar to previous findings [5,6], the descriptive results presenting mean scores on LS were in the positive range, with scores above the neutral point of the scale (mean score ≥ 20) at all three time points; the highest score was in 2016. Multivariate results from the linear regression analysis showed that time was significantly associated with LS, with a significantly higher score found for adolescents in 2016 compared with those in 2011 when controlling for sex and age. However, no significant differences were found when controlling for selfrated health and stress domains, which is the main result to be interpreted. No differences in LS were found between 2022 and 2011. The findings are in line with previous studies on adolescents showing generally high mean scores on LS, varying between 23.0 and 25.0 [27]. The present findings contribute to the understanding that LS is perceived as stable by adolescents across time points investigated and are interesting to compare with the Nordic study [9], which showed high levels of LS, especially in Norwegian adolescents 11–15 years old from 2010 to 2014; however, variations in levels of LS were found among the different countries compared. The present findings correspond with studies among adolescents in high-income countries showing small declines or stable levels in LS [14,15]. However, the findings differ from trends in the adult population, showing increasing level of LS across time [1]. Regarding the demographic variables, a significant curvilinear association was found between age and LS, where LS decreased slightly with age between 13 and 18 and increased from the age of 19 to 20 years. Furthermore, boys scored significantly higher on LS than girls when controlled for age, but not when controlled for stress domains and self-rated health. The findings correspond with previous studies showing that sociodemographic factors contribute modestly to adolescents' reported LS, although variations are normal during adolescence [6,9]. The present study findings of the relatively stable levels of LS are interesting based on previous studies showing an increasing prevalence of self-reported mental health problems during the last decade, especially for girls [10,11], in addition to increasing levels of stress experience [24] and psychosomatic health problems during adolescence [12,36,37].

Of the variables investigated in the present study, all stressor domains were strongly negatively associated with LS; the most strongly related in the multivariate linear regression model were stress due to peer pressure and the home environment and stressors in the school context. Furthermore, significant interaction effects of sex by peer pressure, home life, school attendance, and school performance were found. The strength of the associations was especially strong for girls when controlling for age, time, and self-rated health, indicating that the interpersonal and school-related stressors impact girls' and boys' perceptions of LS differently. The present findings of a negative association between stressors and LS are in line with related studies showing that the experience of cumulative and simultaneous stressors, especially those in an interpersonal context, affects adolescents' mental health and wellbeing [24,38]. The findings are also in line with previous studies showing that stressors in the school context are relevant for adolescents' LS [14,24].

The present study findings extend prior research by providing insights into the relatively stable level of LS in the adolescent samples investigated across time points. The findings also contribute by showing the significant role of interpersonal and school-related stressors in association with LS when demographic variables and self-rated health are controlled. An implication of the study is to use the results as a knowledge base in strategies to facilitate positive coping in adolescents' daily life contexts (home/family, community, leisure time, and school). Implementing such strategies relies on cross-sectorial collaboration and integration into different developmental contexts in adolescents' lives. School is one important context for adolescents' positive development and wellbeing with the possibility to work on health-promoting approaches. In the school context, it is possible to work on the school climate and the learning environment as well as students' socioemotional skills through whole-school approaches, where school professionals and school health services are involved [39].

#### *Strengths and Limitations*

This study was based on three surveys conducted in 2011, 2016, and 2022 in public schools in Mid-Norway using the same previously validated instruments. This allowed us to investigate cross-sectional trends over a 10-year period. The sample size from 2022 was relatively small compared with 2016 and 2011, resulting from COVID-19-related restrictions. Although the same municipalities participated in the three samples, some of the participating schools differed across the sub-samples/study years. Adolescents' perceptions of LS are likely to be affected by a range of personal and contextual factors; therefore, it is plausible that other variables in addition to those included (e.g., socioeconomic status, mental health distress, and personality factors) are equally important in accounting for variance in adolescents' perceptions of LS. This was a correlational study and causal conclusions cannot be drawn. A longitudinal design would have allowed the investigation of within-person changes in LS over time. Although self-reporting is a well-used method for assessing subjective phenomena in adolescents, it may also present potential challenges with reference to self-report bias (social desirability and over- and under-reporting). However, the large sample size may contribute to protecting from the influences of potential bias related to sample selection and self-report.
