The extent to which these types of studies yield findings that can be replicated and ultimately advance our understanding of the endophenotype and its associated disorder remains to be seen. However, they can certainly be used to confirm the construct validity of endophenotypes. The gain in power that derives from testing a small number of well-validated markers, or a single risk score based on many markers in aggregate, increases power to detect whether and how two phenotypes are related, although at the expense of being able to identify specific biological mechanisms. Moreover, molecular-genetic researchers are developing ways to optimize polygenic risk scores (e.g., Vilhjalmsson et al., 2015), which should make them ever more powerful. Psychophysiological researchers can contribute to this type of endeavor in a unique way by developing endophenotype risk scores. For instance, a P300 amplitude reduction (P3AR) “risk score” might be developed from GWAS or meta-analytic results and tested for its association with externalizing disorders, which would provide even more direct evidence of the validity of the notion that P3AR is an endophenotype for externalizing psychopathology (W. G.
