Data on lifetime cannabis use was available on cases and controls. In the cases, subjects who reported a lifetime history of 21 or more instances of cannabis use in a single year were queried about their age at first cannabis use as well DSM-IV abuse criteria. Those endorsing a single abuse criterion were subsequently queried for the 6 DSM-IV dependence criteria as well as cannabis withdrawal. Age at meeting criteria for, and recency of, DSM-IV cannabis abuse/dependence were also available.
