The Index was developed by Zill and Peterson, based on numerous preexisting instruments (Achenbach & Edelbrock, 1981; Graham & Rutter, 1968a; Kellam, Branch, Agorwal, & Ensminger, 1975; Langner et al., 1976; Rutter, Tizard, & Whitmore, 1970; National Center for Health Statistics, 1971).