Item response model validation of the German ICD-11 International Trauma Questionnaire for PTSD and CPTSD

Background: In the 11th revision of the International Classification of Diseases (ICD-11) posttraumatic stress disorder (PTSD) and the complex variant (CPTSD) were newly conceptualised. The International Trauma Questionnaire (ITQ) was developed as a brief self-report measure to screen for both disorders. The English original version has been rigorously tested and presents convincing psychometric properties. The aim of the current study was to validate the German version by means of item response theory (IRT). Method: This is a secondary analysis of a representative, trauma-exposed adult sample from the German general population (N = 500). 1- and 2-parameter logistic IRT models (i.e. examination on an item level), diagnostic rates and confirmatory factor analyses were calculated. Results: All items showed good model fit and acceptable to good performance aligning with the items of the English original except for item C1 (Long time to calm down) which had a high endorsement rate and a low discriminatory power yielding low information gain. CPTSD diagnostic rate of 3.2% was lower than in comparable literature. Confirmatory factor analysis deemed the six first-order, two second-order factors model superior. Conclusion: Measurement and factorial validity of the German version of the ITQ was confirmed. The German translation matches the English original in most psychometric properties and can thus be used for research and clinical practice.