In the search for psychopathology-related genes, having an appropriate endophenotype is important for understanding the relationship between genes and behavior. Robust findings in genetic studies searching for gene-phenotype associations are generally hampered by a lack of statistical power due to the fact that a) most subject samples are typically heterogeneous with regard to specific phenotypic characteristics, and b) genes affecting any measured phenotype usually only account for a small proportion of variance of that phenotype (Plomin, 2005; Plomin, Owen, & McGuffin, 1994; Viding & Blakemore, 2007). Also, the route from genes to behavior is typically complex, with multiple biological and cognitive pathways converging on the same behavioral phenotype (Viding & Blakemore, 2007).
