Defining and Measuring Complex PTSD: A Comparison of the International Trauma Questionnaire and the Self-Report Inventory for Disorders of Extreme Stress

Abstract

The inclusion of complex posttraumatic stress disorder (CPTSD) in the eleventh edition of the International Classification of Diseases (ICD-11) was a landmark development for the field of traumatic stress. This followed decades of iterations of proposed diagnostic criteria, beginning with Herman’s (1992a) foundational conceptualization of CPTSD and continuing with disorders of extreme stress not otherwise specified (DESNOS), which was proposed and evaluated for inclusion in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Aligned with the guiding principle of ICD-11 that diagnostic criteria for mental disorders be limited to core symptomatology in order to improve clinical utility, CPTSD in ICD-11 is narrower than previous conceptualizations of CPTSD. The present study sought to examine shared and distinctive aspects of DESNOS and ICD-11 CPTSD, as measured by the Self-Report Inventory for Disorders of Extreme Stress (SIDES-SR) and the International Trauma Questionnaire (ITQ), respectively. These contrasting conceptualizations of CPTSD were compared through a categorical diagnostic approach (i.e., examining diagnostic agreement and differential symptom patterns between diagnostic groups) and a dimensional measurement-based approach (i.e., assessing the convergent and discriminant validity and incremental predictive validity of the SIDES-SR and ITQ). Participants were trauma-exposed college students (N = 743) who completed a large battery of questionnaires, including the SIDES-SR and ITQ. Analyses for the categorical aim demonstrated differential prevalence rates of CPTSD as derived from the two measures, fair diagnostic agreement at the full-scale level, and group differences on external symptom measures (e.g., PTSD, dissociation, suicidality, self-harm, relationship disturbance), with those meeting criteria for both the SIDES-SR and the ITQ generally demonstrating higher symptom severity than those who met for the ITQ alone. Analyses for the dimensional aim demonstrated generally comparable levels of association with external measures of some domains of CPTSD (e.g., relationship disturbance), but stronger levels of association for the SIDES-SR relative to the ITQ for other domains of CPTSD (e.g., dissociation). Additionally, results of multiple hierarchical regressions demonstrated that the SIDES-SR accounted for additional unique variance in external measures of domains of CPTSD beyond that explained by the ITQ, even for domains included in the ITQ (e.g., affect dysregulation). Overall, the results suggest that the ITQ could benefit from expansion to include additional symptoms of CPTSD, such as that reflecting a greater severity of affect dysregulation. Additional findings and implications are discussed.