have otherwise promoted substance use (Hussong et al., 2011). In fact, a prior study of these data show similar protective effects of a score assessing difficulties with family and peers on age of onset of alcohol use (Kuperman et al., 2013). This hypothesis is also supported by the stronger correlation between MDD and SI (r = 0.74) rather than SA (r = 0.52). Alternatively, those with early SI (or MDD, OR = 0.47 – 0.71; Tables S6 and S7) may be at greater risk for very early, but not later, onset of substance use. In other words, these findings may support the idea that early SI is preceded by even earlier substance use and is unlikely to be a “predictor” of it. In addition, this finding may also be sample-specific. Individuals in COGA are at high genetic and environmental liability for onset of substance use; thus, if SI precedes this expected behavior of substance use, it may reflect a developmental pattern of psychopathology that does not increase risk for substance-related onsets.
