In this paper, we have examined the cumulative incidence (sometimes referred to as “lifetime prevalence”) of use—this includes both experimental and heavier use. We also focused upon cumulative incident use rather than past year prevalence of use. Detailed examinations of prevalent (past year) use, and of transitions to dependent use of these drugs, were beyond the scope of the present paper, but are of obvious interest and importance. These are the subjects of future work currently being undertaken.
