The TLI quantifies the component of SUD liability correlating across generations (Rice, Cloninger, & Reich, 1980; Vanyukov, Kirisci, et al., 2003; Vanyukov, Tarter, et al., 2003). It was derived from items contained in 24 psychological and psychiatric instruments administered to parents, teachers, and participants at the baseline (age 10 to 12) evaluation. Studies of twins have revealed that between 75% (Hicks, Iacono, & McGue, 2012) and 85% (Vanyukov et al., 2009) of TLI variance is genetic. At the outset, items were selected according to their face validity and assigned to constructs that have been documented in the empirical literature as associated with development of SUD (see Vanyukov, Tarter, et al., 2003, for review). Next, exploratory (EFA) and confirmatory (CFA) factor analysis documented construct validity of each factor. The items of constructs that discriminated children of SUD+ and SUD− fathers were then submitted to EFA and CFA. Lastly, item response theory (IRT) analysis was performed to obtain the threshold and discrimination parameter of each item and to derive the TLI. The items of the TLI, along with scoring criteria, informant, and
