Given the high levels of criteria endorsement, long-term opioid dependence and other substance dependence observed in this sample it is likely that these participants represent the most severe end of the spectrum. As such, it is not surprising to find such high levels of co-occurring substance dependence and ASPD. Nevertheless, the prevalence of internalizing disorders in the current study was also high and these disorders were not associated with membership of the more severely dependent group; nor did they vary within class as severity increased. Given this, one might speculate that there are different determinants of internalizing and externalizing problems in this population. Nonetheless Krueger and others have found that there is considerable correlation between the externalizing and internalizing dimensions [10, 11, 50].
