Validation of the International Trauma Interview (ITI) for the Clinical Assessment of ICD-11 Posttraumatic Stress Disorder (PTSD) and Complex PTSD (CPTSD) in a Lithuanian Sample

Background: The 11 ^th revision of the International Classification of Diseases (ICD-11) includes a new diagnosis of complex posttraumatic stress disorder (CPTSD). The International Trauma Interview (ITI) is a novel clinician-administered diagnostic interview for the assessment of ICD-11 PTSD and CPTSD. Objective: The aim of this study was to evaluate the psychometric properties of the ITI in a Lithuanian sample in relation to interrater agreement, latent structure, internal reliability, as well as convergent and discriminant validity. Method: In total, 103 adults with a history of various traumatic experiences participated in the study. The sample was predominantly female (83.5%), with a mean age of 32.64 years (SD = 9.36). For the assessment of ICD-11 PTSD and CPTSD, the ITI and the self-report International Trauma Questionnaire (ITQ) were used. Mental health indicators, such as depression, anxiety, and dissociation, were measured using self-report questionnaires. The latent structure of the ITI was evaluated using confirmatory factor analysis (CFA). In order to test the convergent and discriminant validity of the ITI we conducted a structural equation model (SEM). Results: Overall, based on the ITI, 18.4% of participants fulfilled diagnostic criteria for PTSD and 21.4% for CPTSD. A second-order two-factor CFA model of the ITI PTSD and disturbances in self-organization (DSO) symptoms demonstrated a good fit. The associations with various mental health indicators supported the convergent and discriminant validity of the ITI. The clinician-administered ITI and self-report ITQ had poor to moderate diagnostic agreement across different symptom clusters. Conclusion: The ITI is a reliable and valid tool for assessing and diagnosing ICD-11 PTSD and CPTSD.