In order to empirically explore the extent to which the EXT-related genetic influences were shared or unique among the three candidate endophenotypes, we performed multivariate biometric models using a Cholesky parameterization. Biometric models revealed that a substantial portion of the variance in each of these candidate endophenotypes was due to additive genes. Further, there was a significant (although modest) amount of genetic variance that was shared between EXT and each endophenotype, as well as between the endophenotypes themselves. Genetic correlations were strong within the ERP domain (i.e. between P3 and TF-PC1) for both genders, and were moderate across domains (i.e. between ERP measures and beta), being about twice as strong for males as for females. The only exception to these results was the non-significant P3-EXT correlation in females.
