Abstract
<title>Abstract</title> <p> <bold>Background</bold> Problematic internet use among children and adolescents frequently accompanies neurodevelopmental traits, internalizing symptoms, and circadian disruption. We aimed to identify and compare independent correlates of internet addiction (IA) severity with parent-rated time-specific functioning in a child psychiatry registry. <bold>Methods</bold> We analyzed a cross-sectional clinical registry of 1,322 outpatients (mean age 11.3 years, SD = 2.8; 48.3% male) at a national child and adolescent psychiatry center. The Internet Addiction Test (IAT; mean 43.0, SD = 18.1) quantified IA severity. Univariable correlations were calculated using the maximum available data for each variable pair. Independent correlates of IAT scores were examined using a complete-case multivariable ordinary least-squares regression model restricted to participants with complete data across all model variables (n = 612). <bold>Results</bold> In the multivariable model (R² = 0.322; adjusted R² = 0.301), ADHD-RS (β = 0.276, 95% CI 0.178 to 0.374, p < .001) and later bedtime (β = 0.264, 95% CI 0.174 to 0.354, p < .001) were the strongest independent correlates. DSRS-C, OCD symptoms, physical injury fears, and separation anxiety also showed independent associations. In univariable analyses, higher IAT scores were associated with lower QCD functioning scores across all five time bands. The strongest inverse association was observed for QCD Nighttime (r = -0.191, 95% CI -0.244 to -0.137, p < .001). <bold>Conclusions</bold> These findings suggest that IA severity is linked to neurodevelopmental symptoms, sleep timing, and time-specific functional difficulties, although longitudinal and multi-informant studies are needed to clarify directionality and informant effects. </p>