The bivariate association between P3 amplitude and externalizing behavior among EA and AA young adults was significant (rEA = −0.09; rAA = −0.08). In the regression model including age and sex as covariates, P3 amplitude maintained the significant association with externalizing behavior among EA (BEA = −0.01, βEA = −0.05, 95% CI −0.09 to −0.01, ΔR2 = 0.002, 95% CI 0.00–0.01) but not AA individuals (BAA = 0.00, βAA = −0.01, 95% CI −0.07 to 0.05, ΔR2 = 0.00, 95% CI −0.00 to 0.00; Table 2, Fig. 1a, b). As previously reported, there was a significant main effect of sex (βEA = −0.26, 95% CI −0.30 to −0.21; βAA = −0.31, 95% CI −0.38 to −0.25), such that males scored higher on externalizing behavior; however, both P3 by sex interactions were non-significant (βEA = 0.02, 95% CI −0.02 to 0.06; βAA = 0.05, 95% CI −0.01 to 0.11; online Supplementary Table 3).
