use progresses within each drug class. From this latter perspective, substance use progression within a drug class is viewed as transitions from initiation, continuation, and maintenance/escalation of use, to cycles of regression, cessation, and relapse (Clayton, 1992). Furthermore, progression within a class, using dimensional measures such as quantity and frequency of substance use, may predict progression to other classes of substance use and patterns of poly-substance use (Clayton, 1992; Clark et al. 2005). Similar to suicidal behavior assessments, we recommend assessments of both sequential (categorical) and progressive (dimensional) use patterns for adolescent substance use involvement.
