The final study sample included 1847 twin individuals (51% male) with data on at least one variable. Participants were aged between 14.0 and 15.0 years at time of the first survey (M=14.2, SD=0.15) and between 19.9 and 26.6 at the second survey (M=22.4, SD=0.7). The overall sample included 910 complete twin pairs (181 MZ males, 184 MZ females, 152 DZ males, 128 DZ females, and 265 DZ opposite-sex pairs) and 27 single twins whose co-twin did not participate. Single twins were included because they contribute to the estimation of the thresholds. Note that sample sizes differ per variable. Table 1 shows the descriptive statistics for conduct symptoms and each of the substance use variables.
