Although the severity rankings of the criteria were not totally identical across substances, the abuse criteria tended to be more severe than the dependence criteria, while craving was among the least severe (indicating higher prevalence) across all four substances. To quantify the similarity in severity ranking of the criteria across substances, we computed Spearman correlations of the rankings. For alcohol, cocaine and heroin, these correlations were high (alcohol with cocaine, 0.80; alcohol with heroin, 0.78; cocaine with heroin, 0.82), indicating that the criteria had similar patterns of severity for these substances. In contrast, the corresponding correlations for cannabis were more modest (cannabis with alcohol, 0.21; cannabis with cocaine, 0.40; cannabis with heroin, 0.49),driven predominately by the “hazardous use” variable, which was less severe (i.e. more prevalent) for cannabis than in the other substances. In IRT models that included legal problems, the associated severity and discrimination parameters for legal problem were: alcohol (severity = 3.25, discr = 1.04); cannabis (severity = 8.9, discr = .68); cocaine (severity = 2.65, discr = 1.35); heroin (severity = 2.02, discr = 1.63).
