More recent studies among patients in the NIDA Clinical Trials Network (CTN) showed good evidence for unidimensionalty and little evidence of differential item functioning by demographic characteristics for DSM-IV alcohol, marijuana, cocaine and opioid dependence (Wu et al., 2009a), but did not include abuse. Other IRT analyses of addiction scales in adult clinical (Kahler et al., 2003; Morey and Hopwood, 2009), twin (Krueger et al., 2004) or mixed convenience samples (Kirisci et al., 2002) did not directly address DSM-5 because the scales included many extraneous items. Only two clinical studies directly addressed the proposed DSM-5 combination of abuse and dependence criteria. Among 372 U.S. northeastern substance abuse patients (Langenbucher et al., 2004), abuse and dependence criteria were unidimensional for alcohol, cannabis and cocaine, but only after removing legal problems and tolerance. Among 1511 opioid-dependent Australian patients, a two-class, one-factor model for opioid abuse and dependence criteria that included legal problems was suggested (Shand et al., 2011), although a well-fitting unidimensional model from these data with only half the parameters appeared more parsimonious (Hasin, 2011). These two studies offered important information
