Polish adaptation and validation of the International Trauma Questionnaire (ITQ) for PTSD and cPTSD according to ICD-11 in non-clinical and clinical samples

<b>Background:</b> The International Trauma Questionnaire (ITQ) is a validated measure supporting the diagnosis of ICD-11 post-traumatic stress disorder (PTSD) and complex PTSD (cPTSD). It has been translated into 35 languages, also into Polish. Due to the lack of information in the literature about its validation, new Polish version has been re-adapted and validated in the Polish non-clinical and clinical samples of the present study.<b>Objective:</b> The study aimed (1) to adapt the ITQ for use in Polish, (2) to assess the construct validity of ICD-11 PTSD and cPTSD in the Polish ITQ, and (3) to examine the convergent and discriminant validity of the Polish ITQ.<b>Method:</b> The study sample comprised of 452 adults: a non-clinical sample, <i>N</i> = 314, (completed the online version of the questionnaire) and a clinical sample, <i>N</i> = 138, (used a pen-and-paper version). Confirmatory Factor Analysis (CFA) and Latent Class Analysis (LCA) were performed to assess the structure of the ITQ.<b>Results:</b> The CFA supported a two-factor second-order model as the best fit to the data. All factor loadings were statistically significant and reached a satisfactory level. Cronbach's alpha for ITQ (<i>α</i> = 0.887), PTSD (<i>α</i> = 0.810) and DSO (<i>α</i> = 0.875) were good. The LPA revealed four classes: (1) a cPTSD class with elevated PTSD and DSO symptoms; (2) a PTSD class with elevated PTSD symptoms but low scores on the DSO; (3) a DSO class with elevated DSO symptoms but low scores on the PTSD; and (4) a low symptom class with low scores on all symptoms.<b>Conclusion:</b> The amended Polish ITQ has good internal consistency and psychometric properties. The model is well fitted to differentiating PTSD/cPTSD diagnoses according to ICD-11 and is a reliable measure of support for the making of a PTSD/cPTSD diagnosis in the conduct of clinical interview.