Testing whether posttraumatic stress disorder and major depressive disorder are similar or unique constructs

▶ Symptoms of MDD were endorsed less frequently than symptoms of PTSD-even for symptoms shared between the disorders. ▶ PTSD and MDD items primarily represent a single, underlying dimension. ▶ Removing shared PTSD-MDD symptoms and other dysphoria items, PTSD and MDD items continued to represent a single, underlying dimension.