Although affected status (i.e., individuals with any externalizing diagnosis as shown in Table 2) was initially used as a covariate in the RM-ANOVA model, it was removed from the later analysis which is presented here, as the covariate (i.e., externalizing factor) showed neither a main effect nor any interaction effect with any factors in the model. As the electrophysiology data for the within-subjects factors in the current study did not adhere to the sphericity assumption (i.e., the equality of the variances of the differences between levels of repeated measures factor, such as region), we used multivariate test statistics, which are not dependent on the assumption of sphericity (O’Brien and Kaiser, 1985; Field, 1988). Hence this provides an appropriate alternative method to analyze EEG data with repeated-measures multivariate analyses of variance, which does not assume sphericity and therefore does not require any corrections (cf. Bell and Cuevas, 2012). Bonferroni adjusted pairwise comparisons within each significant main and interaction effects were analyzed using estimated marginal means (EMM) and standard errors (SE). The BIS scores between LR and HR groups were analyzed using one-way ANOVA. The relationship between P3 amplitudes and BIS scores was examined using Pearson correlation coefficients.
