Several studies have used latent class analysis (LCA) to characterize the co-occurrence of psychiatric disorders (Kessler et al., 2005). Results from LCA of DSM-IV disorders in adults from the National Comorbidity Survey Replication (NCS-R) suggested there were classes of pure externalizing disorders, pure internalizing disorders and comorbid internalizing and externalizing disorders (Kessler et al., 2005). Subsequent analysis of the NCS and NCS-R data identified classes that could similarly be distinguished by the clustering of internalizing disorders, externalizing disorders, and by the comorbidity of internalizing and externalizing disorders (Vaidyanathan et al., 2011). Overall, the evidence from these and additional reports from other cohorts (Sullivan, 1998; Olino et al., 2012; Todorov et al., 2006, Dawson et al., 2010) support several comorbidity subtypes that typically encompass unaffected, internalizing, externalizing, and highly comorbid patterns of SUD and psychiatric disorders.
