Interplay of mobile phone dependency and catch-up sleep in South Korean youth: A seven-wave study of two nationally representative cohorts

This study investigated the reciprocal loop between catch-up sleep and mobile phone dependency from late childhood to late adolescence, distinguishing between inter-individual and intra-individual variations. Data from two nationally representative South Korean birth cohorts (N = 4,729, 48.8% female) were collected annually, assessing participants seven times from Grade 4 to Grade 10 or Grade 7 to post-high school. Findings from a cross-lagged panel model (CLPM) and a random-intercept CLPM showed that students who were more dependent on their mobile phones, either compared to others or to their own averages, were likely to report greater catch-up sleep from Grade 4 through Grade 7 in the younger cohort and from Grade 7 through Grade 10 in the older cohort. Likewise, students with greater catch-up sleep, compared to others or to their own averages, tended to rely more on their mobile phones from Grade 4 to Grade 5 in the younger cohort and from Grade 7 to Grade 8 in the older cohort. The CLPM findings further revealed that in the younger cohort, students with higher mobile phone dependency than their peers were more likely to increase catch-up sleep from Grade 7 to Grade 8, and in the older cohort, from Grade 10 to Grade 11. Similarly, higher catch-up sleep led to increased mobile phone dependency from Grade 9 to Grade 10 in the younger cohort, and from Grade 12 to the year post-high school in the older cohort. These patterns suggest consistent tendencies at both inter- and intra-adolescent levels.