Somatic symptom and related disorders have been difficult to study from an epidemiological perspective compared with other mental health disorders. Difficulties stem from two issues. First, somatic symptom and related disorders as a group have undergone more changes in the past 30 years with respect to nomenclature and diagnosis than other mental health disorders. Epidemiological investigations have, therefore, often excluded these [Page 3276]conditions due to uncertainty about how they are classified or diagnosed. Second, the diagnosis of somatic symptom and related disorders has historically depended on ruling out medical conditions that could possibly cause distressing physical symptoms. The scientific effort needed to systematically and comprehensively assess both the body and the mind on a large scale has made the epidemiological study of these disorders impractical; ...