Despite the significant contributions from previous studies, important questions remain regarding the factors influencing transition from substance use to dependence. For example, most studies have examined all substances together (Kessler et al., 2001; Merikangas et al., 1998) or focused on a single substance (Breslau et al., 2001; Chen et al., 2005; O'Brien and Anthony, 2005), precluding formal examination of similarities and differences of predictors across substances. Psychiatric comorbidity, a consistent predictor of transition in many studies (Kessler et al., 1997; Merikangas et al., 1998) has been often examined as a single category (Merikangas et al., 1998) or analyzed as invariant over time (Breslau, 1995; Sintov et al., 2009). Few studies have examined racial-ethnic differences in the rates and determinants of transitioning from use to dependence (Grant, 1996; Grant et al., 2004b; Kandel et al., 1997; Ridenour et al., 2005).
