Diagnostic criteria for abuse and dependence were not included in the SSAGA interview. Therefore, we used the following assessments of illicit drug use: (f) Quantitative cannabis use: An ordinal measure of cannabis use was created from the participant's report of how often in their entire lifetime they had used cannabis. Participants could respond with any number, but were also given the option of responding “Too many times to count” which was assumed to be greater than 950. These responses were then collapsed into a five category ordinal scale, defined separately for males and females. For males these categories were 1−2 times, 3−9, 10−49, 50−499, 500+; for females they were 1 time, 2−4 times, 5−11, 12−99, 100+. Frequency was also coded in all participants, including lifetime abstainers, who were coded as 0.(g) Other illicit drug use: A dichotomous item reflecting whether the participant had used an illicit drug other than cannabis, including cocaine, stimulants, sedatives, opiates, solvents, hallucinogens, phencyclidine (PCP) or other illicit drugs, even once in their lifetime.(h) Drug problems: A dichotomous item assessing severe liability to drug abuse/dependence was
