Our second, independent sample was FinnTwin12 [24]—a population-based twin sample identified through Finland’s Population Register Center. Approximately 2700 pairs of twins were initially enrolled between ages 11–12 and have been contacted for multiple follow-up assessments of behavioral, emotional, and physical health. In the present study we used data from 1162 participants (467 MZ individuals, 684 DZ individuals, and 11 individuals of unknown zygosity; 53% female, 47% male) for whom there were genome-wide association (GWA) data. Relevant phenotypic data from a psychiatric interview and self-report measures of parental knowledge (n = 1115) and peer deviance (n = 1116) at age 14 were available for a subset of the GWA sample.
