| Description |
Digital media use has been found to be a salient factor for worsened sleep outcomes and consequent impairment in daily functioning among adolescents. Prior evidence is largely cross-sectional. Despite the growing number of longitudinal research, it mainly focused on the effects of digital media use on sleep-related outcomes. Only a few studies considered the opposite direction of the association, yielding mixed findings (e.g., Mazzer et al., 2018). Tri-variate analyses that also consider some subsequent sleep-related outcomes, such as daytime sleepiness, are even rarer (for meta-analysis, see Sagano et al., 2023). Moreover, many such studies relied on the cross-lagged panel model (CLPM), the statistic modelling strategy that conflates between- and within-person variance in observed variables and thus may lead to erroneous conclusions regarding causally dominant variables in the underlying causal pattern (Hamaker et al., 2015). Therefore, there is a lack of studies evaluating bi-directional longitudinal associations among digital media use, sleep, and sleep-related outcomes with a particular focus on distinguishing stable traits from individual change over time. The current study is the first study to examine reciprocal associations between screen time, bedtime, and daytime sleepiness – the understudied (Sagano et al., 2023), yet potentially important mediator of various adverse effects of sleep impairment such as worsened performance in school (Dewald et al., 2012) or sedentary behaviour (Kim et al., 2020). The second aim is to examine the moderating effect of reducing screen time before bedtime – a common sleep-friendly recommendation (Hale et al., 2018). To achieve these aims, the current study utilizes the multiple group RI-CLPM and analyses data from a three-wave, one-year-long panel study based on the representative sample of Czech adolescents aged 11-16 (N=2,500, Mage = 13.43, 50% girls at Wave 1). The preliminary analyses showed stable, trait-like differences between adolescents in all observed variables. Concerning the within-person effects, later bedtime at T2 was associated with higher screentime at T3. Carry-over autoregressive effects were found for all three variables but only between T2 and T3. Concerning the between-person effects, adolescents who typically spent more time with screens during the day went to bed later and reported higher daytime sleepiness. In addition, adolescents who typically went to bed later reported higher daytime sleepiness. The multiple group analysis did not find a moderating effect of reducing screen time before bedtime. The current study's findings contribute to existing knowledge, showing that stable between-person differences in screen time, not within-person processes, explain the associations between digital media use, sleep, and associated sleep outcomes. These findings also have important societal implications: Because the analysis did not find statistically significant group differences between adolescents who reduce screen time before bedtime and those who do not, reducing the typical daily patterns in screen time seems to be a more effective sleep-friendly recommendation for adolescents.
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