Interaction effects in comorbid psychopathology.

PURPOSE Comorbidity in psychopathology is the norm. Despite some initial evidence, few studies have examined if the presence of comorbid conditions changes the expression of the pathology, either through increased severity of the syndrome(s) or by expanding to symptoms beyond the syndrome(s) (i.e., symptom overextension). The following report provides an illustration of interactive effects and overextension in comorbid pathology. METHOD A large pool of patients from a university hospital were assessed using SCID-I/P interviews. Of these, 230 patients diagnosed with major depressive disorder, social phobia, or both were included in the study. RESULTS Symptoms not belonging to either index condition (major depressive disorder or social phobia) reliably overextended in comorbid cases (odds ratios between 2.82 and 15.75). CONCLUSIONS Current research methodologies (e.g., structured interviews) do not allow for the examination of overextended symptoms. The authors make a call for future psychopathological research to search systematically for interactive effects by adopting more inclusive or flexible assessments.