Abstract
BACKGROUND: Anxiety and depression are among the most prevalent mental health disorders in adolescence. However, there is a lack of efficient instruments that simultaneously assess both the severity and impairment associated with these symptoms. This study aims to adapt and further validate the Overall Anxiety Severity and Impairment Scale (OASIS) and the Overall Depression Severity and Impairment Scale (ODSIS) for adolescents. METHODS: The psychometric properties of the OASIS-A and ODSIS-A were examined in a community sample of 598 adolescents (51% male) from Portuguese public schools. Analyses included factor structure, internal consistency, measurement invariance, construct validity, gender-based comparisons and cutoff scores. RESULTS: Factor analysis supported a unidimensional structure for both the OASIS-A and ODSIS-A. The internal consistency was excellent for both scales (Cronbach's α and McDonald's ω for the OASIS-A were 0.90 and for ODSIS-A were 0.94) and measurement invariance across gender was established. The OASIS-A and ODSIS-A showed significant correlations with measures of anxiety, depression, quality of life and mental well-being, in theoretically expected directions. Additionally, girls reported significantly higher levels of anxiety and depression. Optimal cutoff scores were identified as 7 for OASIS-A and 5 for ODSIS-A. CONCLUSIONS: This study presents the first psychometric evaluation of the OASIS-A and ODSIS-A, underscoring the utility of brief self-report measures for the severity and impairment associated with anxiety and depression in adolescents. Findings also support the use of these tools for screening purposes, particularly in school settings.