We investigated whether abuse and dependence criteria follow a single dimension or are better modeled as two separate dimensions several ways. Following conventional methods, we first examined the eigenvalues obtained from the tetrachoric correlations of all 11 criteria (10 criteria for cannabis). A single dimension is supported with one large eigenvalue and a large ratio of the first to second eigenvalue (Hutten, 1980; Lord, 1980). Second, we fit a 2-factor confirmatory factor analysis (CFA) model with abuse and dependence criteria on separate factors and estimated the correlation between them. Correlations between factors exceeding 0.85 suggest combining them into a single dimension (Brown, 2006). Third, we considered a useful complement to traditional dimensionality analyses called the confirmatory bifactor model which examines the evidence for items as measures of a single overall “general” factor vs. subgroups of items forming subscalesmeasuring distinct “group” factors (Reise et al., 2007). Specifically, the bifactor model assumes each criterion loads on two factors, one overall “general” factor (shared by all criteria) and another “group” factor shared only by those other criteria potentially measuring the same (sub) construct.
