Development and psychometric validation of the Kanazawa University loneliness scale for children and adolescents

Loneliness is a key risk factor for youth mental health; however, existing scales often fail to capture its multidimensional and relational nature. This study developed the blinded University Loneliness Scale (KULoS) for students in Grades 1-9 and evaluated its psychometric properties using cross-sectional and longitudinal survey data collected in Ishikawa, Japan (Time 1: n = 856; Time 2: n = 709). Exploratory factor analyses conducted separately for grades 1-4 and grades 5-9 supported a two-factor structure primarily reflecting item wording (direct vs. indirect items). The four-item direct subscale (KULoS-D) demonstrated good internal consistency (ω = 0.801-0.862), whereas the indirect subscale (KULoS-I) showed lower reliability (ω = 0.662-0.666). Confirmatory factor analyses at both time points indicated a good fit for the two-factor model. KULoS-D showed strong associations with single-item loneliness and depressive symptoms (rs ≈ 0.50) and moderate correlations with aggressive and prosocial behavior in the expected directions, whereas KULoS-I demonstrated weaker convergent and criterion-related validity. Cross-lagged panel analyses revealed that KULoS-D at Time 1 significantly predicted depressive symptoms at Time 2 after controlling for baseline depressive symptoms, whereas KULoS-I did not predict depressive symptoms. Overall, these findings support the KULoS-D as a brief and psychometrically robust measure of loneliness in children and early adolescents, with potential utility for large-scale research and early screening.