37.5% of the sample reported having never tried cannabis. Non-abstainers in both cohorts were queried, “How old were you the first time you used cannabis?” Responses ranged from 6 to 34 years. The variable reasonably approximated a normal distribution (skewness=0.99, kurtosis=1.25). Reported ages of cannabis initiation were 18.9 years in Cohort II and 17.9 years in Cohort III. Mean ages of first cannabis use in Cohort II were 18.7 years (SD=3.2) for men and 19.2 years (SD=3.5) for women, and in Cohort III were 17.6 years (SD=3.2) for men and 18.1 years (SD=3.5) for women.3 Retest data indicated good reliability in recall (r(117)=.80, p<.0001). The correlation between age and reported age at first cannabis use (r=.08) was slightly higher than for the ages of tobacco and alcohol initiation, but still small, suggesting limited age-related bias. The age of cannabis initiation was negatively associated with birth year (r=−.19) and assessment year (r=−.13).
