The finding of stronger within-class than between-class predictive associations is consistent with previous longitudinal studies of prevalent disorders among youth (Costello et al., 2003; Newman et al., 1996; Reinke & Ostrander, 2008), although we are unaware of previous comparable studies of first onset of lifetime disorders. Comparable results were also found in our previous cross-national study of the development of comorbidity among adults (Kessler et al., 2011). The finding that fear disorders are the most important between-class predictors is consistent with, but goes beyond, previous research showing that early-onset anxiety disorders predict later distress disorders (Costello et al., 2003; Lewinsohn et al., 1995; Pine et al., 1998; Stein et al., 2001). Substance use disorders, at the other extreme, generally do not predict later disorders but are predicted strongly by earlier disorders. Although associations of behavior disorders with later substance disorders are well-documented (Costello et al., 1999; Fergusson et al., 2007), the predictive associations of primary fear and distress disorders have been less consistently examined (Costello et al., 2003).
