Studies were included if the following criteria were met: OCD diagnosis was assessed using standardized and validated instruments, or by a population database record (based on the Diagnostic and Statistical Manual of Mental Disorders [DSM-III or DSM-III-R, or DSM-IV, or DSM 5], or the International Classification of Diseases, Eight, Ninth or 10th Revision [ICD-8, ICD-9 or ICD-10] diagnostic criteria); the probands were diagnosed with OCD by direct interviews; relatives were directly interviewed; the study designs comprised cohort or case-control studies; and included a control group.
