Comorbidity of psychiatric and substance use disorders in late adolescence: A cluster analytic approach

Cluster analysis was used to identify subgroups of youths with past-year su bstance and/or psychiatric disorders (N = 110, mean age 19.0 years). Data f or this study came from a community-based, prospective longitudinal investi gation of speech/language (S/L) impaired children and matched controls who participated in extensive diagnostic and psychosocial assessments at entry into the study at 5 years of age and again at follow-up. Clustering variabl es were based on five DSM diagnostic categories assessed at age 19 with the University of Michigan Composite International Diagnostic Interview. Using Ward's method, the five binary variables were entered into a hierarchical cluster analysis. An iterative clustering method (K-means) was then used to refine the Ward solution. Finally, a series of analyses of variance (ANOVA s) were run to analyze group differences between clusters on measures of Gl obal Assessment of Functioning (GAF), criminal involvement, anxiety and dep ressive symptomatology, and frequency of drug use and heavy drinking. The a nalysis yielded eight replicablc cluster groups, which were labeled as foll ows: (a) anxious (20.9%); (b) anxious drinkers (5.5%); (c) depressed (16.4% ); (d) depressed drug abusers (10%); (e) antisocial (16.4%); (f) antisocial drinkers (10%); (g) drug abusers (8.2%); (h) problem drinkers (12.7%). The se groups were differentiated by external criteria, thus supporting the val idity of our cluster solution. Cluster membership was associated with a his tory of S/L impairment: A large proportion of the depressed drug abusers an d the antisocial cluster group had S/L impairment that was identified at ag e 5. Clarification of the developmental progress of the youths in these clu ster groups can inform our approach to early intervention and treatment.