endorsement of each of the 7 dependence criteria for cocaine and opioids was similar while certain alcohol and cannabis criteria (e.g. tolerance) were endorsed more often than others (e.g. use dominates life). This may be related to the ascertainment strategy and overrepresentation of family history for alcoholism in both samples. Nonetheless, all factor loadings were high, indicating that QUANTDEP reflects a general liability to dependence across multiple substances. In particular, QUANTDEP captures the liability to cocaine and opioid dependence criteria in these two studies. Therefore, in addition to being an index of severity and a measure of general liability to addiction across alcohol and drugs, QUANTDEP likely also reflects variation in prevalence and the expected pattern of comorbid relationships and co-aggregation across alcohol and drug dependence criteria in these subjects ascertained on specific substance dependence.
