Psychometric evaluation of the Inventory of Statements About Self-Injury (ISAS-I) in adolescents: evidence from SEM, Bayesian reliability, and item response theory.

Introduction: Non-suicidal self-injury constitutes a significant mental health issue among adolescents due to its association with depressive symptoms, anxiety, and an increased risk of suicidal behavior. Proper assessment of this behavior is essential for both research and clinical practice; however, in the Peruvian context, there are still limited instruments with solid evidence of validity and reliability. Objective: To analyze the psychometric properties of the Inventory of Statements About Self-Injury (ISAS-I) in Peruvian adolescents. Methods: Psychometric, cross-sectional, basic research with a quantitative approach. A total of 1,249 adolescents (56% male) participated and completed a sociodemographic questionnaire and three psychological instruments. The existing Spanish adaptation of the ISAS-I was used, and its content validity and comprehensibility were examined in the target population. Statistical analyses were conducted using structural equation modeling and item response theory. Results: The ISAS-I demonstrated adequate content validity ( Conclusion: The ISAS-I presents adequate evidence of validity and reliability in Peruvian adolescents, supporting its use as a brief and precise measure for assessing non-suicidal self-injury. These findings should be understood as psychometric evidence for the existing Spanish adaptation of the ISAS-I in this population, rather than as evidence of a new cross-cultural adaptation. Furthermore, its invariance across sex and its associations with mental health indicators support its utility in both clinical and research settings, promoting early detection and the design of preventive strategies in adolescent populations.