Factor structure of the International Trauma Questionnaire in UK Armed Forces veterans residing in Northern Ireland.

: Complex Posttraumatic Stress Disorder (C-PTSD) was recently included in the revised International Classification of Diseases (ICD-11) by the World Health Organization (WHO, 2018). C-PTSD is a new trauma related disorder which may develop after prolonged and multiple exposures to trauma. It is a sister disorder of PTSD and is further characterized by symptomatology of disorganized self-organization (DSO). To qualify for the diagnosis, individuals must first meet the diagnostic criteria for PTSD, then report DSO symptoms and functional impairment. A body of work is emerging which has focused on the underlying dimensionality of C-PTSD across both adult and more recently adolescent populations from differing index trauma groups and from across several nations and cultures. However, few studies have been conducted in populations exposed to combat trauma despite the obvious prolonged and multiple nature of their trauma histories. : To contribute to emerging evidence of the factor structure of ICD-11 C-PTSD in a novel population. : This is the first factor analytic study to explore C-PTSD in a sample of UK Armed Forces veterans residing in Northern Ireland ( = 732). C-PTSD was measured via the ITQ and we utilized CFA to assess the fit of 7 competing models. : Based on established CFA fit indices, a correlated, first order, 6-factor model of C-PTSD, representing 3 PTSD and 3 DSO symptom groupings, was deemed to provide superior fit to the data compared to 6 alternative C-PTSD models. The superiority of the model was further supported by statistical comparisons of competing C-PTSD models. All factor loadings (0.866-0.998) and inter-factor correlations (.746-.975) of the optimally fitting model were statistically significant and high. : These results provide support for the construct validity of ICD-11 C-PTSD in a unique sample of Armed Forces veterans residing in Northern Ireland.