substance use disorders, schizophrenia, and schizophreniform disorders. Those with a stable diagnosis across waves 1 and 2 had lower age of onset and higher rates of depressive and anxiety disorders, substance use and schizophrenia (71). The Singapore national mental health surveys (69, 70) described comorbidity patterns of psychiatric disorders as well as medical disorders. The study from Iran (68) found OCD to be highly comorbid with depressive and anxiety disorders; they also reported prevalence of comorbid severe mental illness (bipolar disorder, schizophrenia) and epilepsy. The British study (66, 67) described various substance use comorbidity patterns and a screening report on personality disorders with OCD. Overall, these studies reported prevalence of depressive disorders, the most common comorbidity, ranging from 14 to 43%. Rates of anxiety disorders varied (Specific phobias: 5–46%, GAD: 5–31%, Social phobia: 8–25%, Panic disorder: 6–26%). The prevalence of schizophrenia was between 2 and 3%, except for a higher prevalence of 17.9% reported in wave I of the ECA study (65). However, this study had a substantially lower number of individuals (<12%) with a “stable” diagnosis of OCD (71). The rates of alcohol and substance use disorders varied widely across studies.
