The Role of Negative Affect in Differentiating Posttraumatic Stress Disorder, Depression, and Their Comorbidity Among United States Veterans.

Following trauma exposure, two frequently co-occurring forms of psychopathology include posttraumatic stress disorder (PTSD) and major depressive disorder (MDD). Although these diagnoses have been identified as distinct constructs, the proper classification of these disorders remains a challenge due to overlapping symptoms. Instead, systematically establishing higher- and lower-order personality traits associated with each diagnosis may avoid this confound and improve differential diagnosis. In the present study, we examined how higher-order negative affect and its lower-order facets (i.e., anxiousness, emotional lability, and separation insecurity) may be associated with a diagnosis of PTSD only, MDD only, both diagnoses, or neither diagnosis. Participants were 1,175 veterans enrolled in the Veterans After Discharge Longitudinal Registry. Higher- and lower-order negative affect were assessed using the Personality Inventory for DSM-5 (PID-5), and PTSD and MDD diagnoses were based on the Structured Clinical Interview for DSM-5 (SCID-5). Multinomial logistic regressions were used to model the association between higher- and lower-order negative affect and diagnostic status, after controlling for potential covariates. Diagnostic utility analyses were conducted to examine the degree to which higher- and lower-order negative affect classified participants across groups. Higher-order negative affect and lower-order anxiousness differentiated diagnostic groups, ORs = 1.76-4.66, and had strong specificity and negative predictive value for individuals with PTSD and MDD and those with MDD only. These findings help explain the role of higher-order negative affect and lower-order anxiousness in differentiating PTSD from MDD and comorbid PTSD and MDD and may have implications for assessment, differential diagnosis, and treatment planning.