The Cholesky model allowed us to further assess the genetic variance shared among various combinations of the candidate endophenotypes and EXT, in order to determine if any endophenotypes shared variance with EXT independent of that shared with the other endophenotypes. Based on the literature, P3 has shown the most robust genetic associations with EXT (e.g. Hicks et al., 2007; Hill et al., 1998; Porjesz & Rangaswamy, 2007), thus we entered P3 into the model first, followed by the P3-associated TF component, the beta power measure, and EXT. For both genders, there was significant genetic variance collectively shared among all the candidate endophenotypes, and for males this genetic variance was also shared with EXT. In males, this shared genetic variance was carried by the relationship between P3 and EXT, as there was no significant variance shared among the remaining endophenotypes and EXT independent of that shared with P3. In females, however, there was no significant genetic variance shared between P3 and EXT, whereas the TF component and beta power did share significant variance with EXT independent of their genetic overlap with P3. Further, the TF component and beta power each had significant independent genetic covariance with EXT in females.
