The approach of the Diagnostic and Statistical Manual of Mental Disorders (DSM) to describing psychopathology makes use of the syndrome perspective, which involves identification of a constellation of symptoms thought to stem from a common cause or thought to indicate a disease or abnormal condition (Kraepelin, 1981). Disorders can include heterogeneous symptoms, as long as the various symptoms reflect a common cause. Thus, a valid syndrome is understood to reflect a homogeneous grouping of individuals (Robins & Guze, 1970). From a syndromal perspective, symptoms within a disorder may not correlate perfectly, even though they sometimes stem from a common cause and indicate a disease process. For example, the experience of headaches, muscle aches, sore throats, and fatigue do not covary perfectly because they can have different causes, but sometimes they occur together due to a common cause and are called the flu.
