Subsequent studies have utilized increasingly larger samples of twins, employed more advanced genetic analysis methods based on linear structural equation modeling and investigated an increasingly broad spectrum of psychophysiological phenotypes. By now, several large-scale studies of psychophysiological phenotypes involving hundreds and even thousands of twins have been conducted, including Free University of Amsterdam (Dorret Boomsma and Eco de Geus), University of Minnesota (William Iacono), University of Southern California (Laura Baker), University of Queensland (Margaret Wright and Narelle Hansell), Washington University in St. Louis (Andrey Anokhin), and other research centers.
