The inability to measure individual risk for SUD, particularly at a young age, hinders etiologic research and prevention. Previous research has developed an index of transmissible liability (TLI)that covers the entire range of liability phenotypes, does not rely on SUD symptoms, is derived from items drawn from psychological and psychopathological instruments, and can be applied in a young or otherwise asymptomatic population. TLI has high heritability and has been validated as a measure of transmissible risk for SUD in previous studies. This index, however, requires information obtained not only from the individuals but also from their parents and teachers. Developing SUD liability indices that do not involve those additional informants could augment the feasibility and efficiency of measurement. One of the goals of this study was to construct new indices based on a reduced number of questionnaire items used to derive the original TLI and determine their utility in measuring risk for SUD. Another purpose of this study was to investigate composition of phenotypic variance of the newly developed liability indices. Participants were self-selected twin pairs attending the 2006, 2007, and 2009 Twins Day Festivals in Twinsburg, OH, and participants in the CEDAR database from the University of Pittsburgh. Results of this research indicate that the ability of the newly developed liability indices to predict SUD is similar to that of the original TLI. Biometrical genetic analysis showed that the phenotypic variance of the new SUD liability indices is comprised of approximately equal additive genetic and unique environmental components. This study has public health relevance as it developed new measurement techniques to identify individuals at high risk of developing SUD, which will be beneficial for prevention and intervention
