These manifold benefits, however, are predicated on the successful identification of endophenotypes and a number of criteria have been proposed to clarify whether a characteristic is appropriately thought of as an endophenotype. Since the initial introduction of the concept almost forty years ago (Gottesman & Shields, 1973), the term was intended to refer to a characteristic or process that was not readily observable, but was significantly associated with the disorder of interest, could be objectively and reliably assessed over time, and was heritable. In addition, further criteria for an endophenotype are evidence that it is state-independent (i.e., present even when the disorder is not) and present in non-affected family members at a higher prevalence than in the population in general, reflecting transmission patterns of familial association and cosegregation (Flint & Munafò, 2007; Gottesman & Gould, 2003). Additional criteria that have been proposed are that an endophenotype be continuous in nature, part of a biologically plausible etiological process, and closer to the genetic causative factors than to the disorder (Flint & Munafò, 2007). Importantly, it has been noted that an endophenotype
