People with post-traumatic stress disorder (PTSD) exhibit negative cognitions, predictive of PTSD severity. The Post-Traumatic Cognitions Inventory (PTCI) is a widely used instrument measuring trauma-related cognitions and beliefs with three subscales: negative thoughts of self (SELF), negative cognitions about the world (WORLD), and self-blame (BLAME).

The current study attempted to validate the use of the PTCI in people with serious mental illness (SMI), who have greater exposure to trauma and elevated rates of PTSD, using confirmatory factor analysis (CFA) and examining convergent and divergent correlations with relevant constructs.

Participants were 432 individuals with SMI and co-occurring PTSD diagnosis based on the Clinician Administered PTSD Scale, who completed PTCI and other clinical ratings.

CFAs provided adequate support for Foa’s three-factor model (SELF, WORLD, BLAME), and adequate support for Sexton’s four-factor model that also included a COPE subscale. Both models achieved measurement invariance at configural, metric and scalar levels for three diagnostic groups: schizophrenia, bipolar and major depression, as well as for ethnicity (White vs Black), and gender (male vs female). Validity of both models was supported by significant correlations between PTCI subscales, and self-reported and clinician assessed PTSD symptoms and associated symptoms.

Findings provide support for the psychometric properties of the PTCI and the conceptualization of Sexton’s four-factor and Foa’s three-factor models of PTCI among individuals diagnosed with SMI (Foa et al., 1999).