Aim: No validated self-report scale is available for use as a screening tool to detect non-help-seeking adolescents at ultra-high risk (UHR) for psychosis in a community setting. The study aims to examine the reliability and validity of the Korean version of the Eppendorf Schizophrenia Inventory (K-ESI) for assessing adolescents at UHR for psychosis in a community setting.

Methods: In the first study, to confirm the reliability and discriminant validity of the K-ESI, community sample (782 adolescents, 281 young adults, 122 early and middle-aged adults) and outpatients with schizophrenia (109) were recruited. A single cross-sectional survey was performed using the K-ESI for the community sample and the K-ESI and Positive and Negative Syndrome Scale for patients. In the second study, the Korean version of Youth Self Report (K-YSR) was administered initially to 1002 students. Of the 217 students whose scores were equal to or higher than the cut-off point of the K-YSR, 120 who agreed to an in-depth evaluation were interviewed using the Comprehensive Assessment of At-Risk Mental States to confirm the predictive validity of the K-ESI. 

Results: The K-ESI showed good internal consistency and excellent testretest reliability and discriminant validity. However, the factor structure in adolescents was substantially different from that of the original ESI. The best cut-off point for the K-ESI to identify UHR adolescents was 29, with a sensitivity of 77% and a specificity of 70%. 

Conclusion: The results revealed that the K-ESI can be used as a valid and reliable instrument to identify adolescents at UHR for psychosis in a community setting.