The main parameters of the study, as determined by the National Advisory Committee on Drugs – Sub-committee on Prevalence, specified that three data sources were to be employed in the study, namely: the Central Drug Treatment List, a national Garda Study on Drugs, Crime and Related Criminal Activity and the Hospital In-patient Enquiry database. Statistically valid estimates of the prevalence of opiate drug use in the national population and by sub-region were required for the years 2000 and 2001.