Results from these studies support the use of broad latent factors to interrogate the shared genetic aetiology of externalizing phenotypes and SUDs. However, the question remains as to whether SUDs and externalizing are influenced by distinct, but related, dimensions of risk, or whether they reflect the same underlying continuum of risk. In other words, is there specific genetic risk shared across SUDs that is not also shared with other externalizing outcomes? To address this question, we applied genomic SEM to six externalizing phenotypes and four SUDs previously included in the factor models of externalizing11 and addiction liability.20,21 We tested a series of a priori specified models, guided by results from the phenotypic factor analysis literature, which have produced inconsistent results with respect to the placement of SUDs in the overall structure of psychopathology. Many studies include SUDs as part of a broad externalizing factor,22–25 whereas others model it as a separate, but correlated, factor.26–29 We tested five alternative confirmatory factor analytic models, including a common factor model and alternative parameterizations of a two-factor structure to capture the genetic covariance among
