In this article, we evaluate this promise and recommend best practices for genetic endophenotype research that we believe can improve the quality of investigation. We are informed in this effort by our own experience conducting molecular-genetic investigations of more than a dozen psychophysiological measures (W. G. Iacono, Malone, Vaidyanathan, & Vrieze, 2014b; Malone et al., 2014; Vaidyanathan, Isen, et al., 2014; Vaidyanathan, Malone, Donnelly, et al., 2014b; Vaidyanathan, Malone, Miller, McGue, & Iacono, 2014; Vrieze et al., 2014a, 2014b), as well as by the lessons of the past decade or so of molecular genetic research, which have prompted researchers to think about the genetics of complex traits and diseases differently. We have learned that disorders like schizophrenia are caused by many genetic variants each of which has a small effect in the general population (Schizophrenia Working Group of the Psychiatric Genomics, 2014). In fact, neurodevelopmental disorders like schizophrenia, which only a few decades ago were thought to be caused primarily by the home rearing environment, are not all that different in their genetic architecture from complex medical diseases like coronary
