g. year of once birth and sex), was also used for eliminating multiple counts when analysing characteristics of unique treatment seekers. Although some double counts will not have been recognised as such, absolute perfection is neither possible nor required [26]. After all, the main purpose was to reduce the probability of the number of multiple counts to a level that is a good estimation of the true number of unique treatment seekers [23]. Furthermore, this method is also advised by the EMCDDA in order to avoid distortion of research results. Instrument Due to the lack of a common registration tool in Belgian substance abuse treatment [27], a specific instrument was developed.

The variables included were largely derived from questions or variables in the ‘Treatment Demand Indicator’ protocol, a common European standard manual on treatment demand registration developed by the Pompidou Group/European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) [23] and from items in the European Addiction Severity Index (EuropASI), a semi-structured interview that offers the possibility for clinicians and researchers to map the severity of functioning problems in various life areas [28,29]. All treatment agencies were involved in the development and elaboration of the instrument and research design in order to enhance participation.

Since this was an additional registration (besides the already existing various administrative registration procedures in each agency), only a limited number of variables was collected: socio-demographic data (sex, age, place of residence, country of birth, employment and living situation); substance-related information (primary drug, regular use of various types of substances); injecting behaviour (ever, during the last 12 months); previous treatment episodes; and type of treatment centre (inpatient vs. outpatient). The primary drug was defined as the drug that – according to the clinician – causes the person the most problems. This definition is in accordance with the guidelines in the EuropASI manual [29]. For data collection purposes, a secure online web application was developed with considerable advantages compared to paper-based registration, e.g. improved data quality and communication between clinicians and researchers. A large majority of treatment centres made use of the application.

Only two treatment centres filled out registration sheets and sent them in on a monthly basis to the researchers due to the fact that internet access was not readily available. Data analysis All data were converted to and entered into SPSS, and a thorough data quality check was performed. If necessary, unclear or contradictory information was passed on to the person in the centre responsible for completion or correction of the registration. Sociodemographic and treatment seeking Anacetrapib differences between five groups (primary drug: alcohol, cannabis, opiate, amphetamine, cocaine) were examined.