for SUDs. This IRT approach assumes that a latent severity trait underlies response patterns of SUDs measured by DSM-IV criteria, and recognizes item-level (criterion) variability in the discrimination and severity of the SUD severity continuum (Saha et al., 2006; Wu et al., 2009a; Wu et al., 2009b; Wu et al., 2009c). IRT analysis determines the unidimensional latent trait underlying criterion symptoms for each disorder (a one-factor syndrome), but also provides vital item-level discrimination and severity estimates for substance-specific criteria (Wu et al., 2009a; Wu et al., 2009b). IRT findings consistently show that dependence symptoms measure various ranges of a “similar” condition underlying SUD problems (Saha et al., 2006; Wu et al., 2009a; Wu et al., 2009b), indicating the presence of poor items and feasibility to identify “core” dependence items for use as a simplified screen for detecting individuals at risk for SUDs. Assuming that an IRT approach to SUDs is feasible, poorly performing items from IRT analysis (low discrimination, high severity) will have low sensitivity/specificity values in identifying individuals with a disorder; reliable items across multiple substances will be good indicators for problematic use that are likely to meet criteria for a SUD.
