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‘Problem drug use’ is defined by the EMCDDA as ‘injecting drug use or long duration or regular use of opiates, cocaine and/or amphetamines’. This definition specifically includes regular or long-term use of prescribed opiates such as methadone but does not include their rare or irregular use nor the use of ecstasy or cannabis. Existing estimates of problem drug use are often limited to opiate and poly-drug use, and so the estimation methods are currently being reviewed to better take account of new phenomena such as potential problems with cannabis.
The methods used to produce prevalence estimates are based mainly on statistical models using drug use related indicators and include mainly:
a simple multiplier method using police, treatment, mortality or HIV/HCV data;
capture–recapture methods;
extrapolation via multivariate indicator methods
The EMCDDA has produced guidelines both for prevalence estimation at local and at national level. At local level the preferred method is a three-(or more)-sample capture-recapture study (though other methods can be used) and detailed guidelines have been produced: Methodological guidelines to estimate the prevalence of problem drug use on the local level. At national level estimates are more difficult to obtain with capture-recapture methods due to spatial heterogeneity of data sets, data availability and quality problems. Draft guidelines have been developed, however, that are currently being updated on the basis of the experience in the Member States.
Given the methodological improvements over the last few years, it seems possible to distinguish between injecting drug users (estimates from overdose mortality or HIV multipliers; these may be mainly current injectors) and the wider group of problem drug users, which includes both injectors and non-injectors.
Available estimates are improving in number and quality, but there are still many problems to be solved. There is not yet one method that can be applied in all the countries to give truly comparable results and even if a standard method such as capture-recapture can be used at local level, available datasets often differ so much that it would be difficult to compare results across countries. Comparability problems also stem from differences in the exact definition of the estimated target group, due to differences in drug use patterns between countries.
Most EU countries were able to produce national estimates of problem drug use using the agreed definition of problem drug use by 2004, although estimates of injecting drug use remain scarce. Many of the available estimates are based on results from more than one estimation method, thereby adding to their reliability.
In addition to local and national prevalence estimation, several countries have been able to explore incidence estimation (time trends in numbers of new cases rather than static estimates of all existing cases) and draft guidelines have been prepared based on two different methods for estimating incidence. In 2005, a new project was started with the aim to provide countries with more guidance and promote more collaboration between them, as well as improvement of quality and implementation of incidence estimation. It involves an e-helpdesk for all interested EU countries.
For more information please contact the EMCDDA or visit http://www.emcdda.europa.eu/?nnodeid=1372
References
EMCDDA and Institut für Therapieforschung. Recommended Draft Technical Tools and Guidelines - Key Epidemiological Indicator: Prevalence of problem drug use. Lisbon: EMCDDA, 2004.
EMCDDA and Centre for Drug Misuse Research. Methodological Guidelines to Estimate the Prevalence of Problem Drug Use on the Local Level. EMCDDA Scientific Report CT.97.EP.05. Lisbon: EMCDDA, 1999.
EMCDDA and University of Tor Vergata. Draft Guidelines for Estimating Incidence. Lisbon: EMCDDA, 2004.
Kraus L, Augustin R, Frischer M, Kümmler P, Uhl A, Wiessing L. Estimating prevalence of problem drug use at national level in countries of the European Union and Norway. Addiction 2003; 98: 471-85.
Smit F, Toet J, van Oers H, Wiessing L. Estimating Local and National Problem Drug Use Prevalence from Demographics. Addiction Research and Theory 2003; 11: 401-413.
Frischer M, Hickman M, Kraus L, Mariani M, Wiessing L. A comparison of different methods for estimating the prevalence of problematic drug misuse in Great Britain. Addiction 2001; 96: 1465-1476.