Participants were drawn from the older cohort of the Minnesota Twin Family Study, a longitudinal community-based sample studying twins and their parents (explained further in Iacono and McGue, 2002). This cohort was initially assessed when the twins were approximately 17 years of age and is almost entirely Caucasian (over 95%; consistent with the demographics for the state of Minnesota at the time the twins were born). At approximate ages of 17, 20, 24, and 29, participants underwent a battery of clinical interviews and psychophysiological measurements. The age-29 assessment included higher-density EEG recording than previous ones. Only participants who visited in-person and had EEG data at their age-29 visit were considered for the present study (N = 434, 199 twin pairs, 36 unmatched twins, mean age = 29.6, standard deviation = 0.6, age range = 28.5 – 31.9).
