Surveillance of Drug Users in Thailand

Conventionally, capture-recapture techniques involving different lists such as police or hospitals are used for quantifying populations which are difficult to count, such as illicit drug user populations. Here, a novel approach is suggested based upon repeated entries in one list, which is less dependent on matching entries from different sources as in the conventional approach. For this purpose, a population-based study will be conducted that utilizes all data on treatment episodes of drug users in Thailand to estimate the size of drug use in the country. The data will stem from the drug treatment surveillance system of the Office of the Narcotics Control Board (ONCB) and cover the period 2000-2003. Based upon the frequency of treatment episodes of each patient, a count distribution will be modelled by means of a Poisson mixture model. Using this count model, an estimate for the number of unobserved drug users can be constructed. The model has been preliminarily tested in a pilot-study with a 3-months time window for Bangkok with excellent results. The Anschubsprojekt will target on investigating which are the possibilities and requirements to achieve access to the full data set on drug users in Thailand. Funding is needed for travelling to Thailand for two scientists.

Capture-Recapture, gemischtes Poissonmodell, Drogenabhängigkeit in Thailand
Head of Project:

Prof. Dr. Dankmar Böhning
Charité - Universitätsmedizin Berlin
Institute of Social Medicine, Epidemiology and Health Economy CCM/CBF
Tel. 8445 1292
Fax 8445 1290
Additional Member of Project:

Dr. Ekkehart Dietz, Ronny Kuhnert
Begin/End of Project:

01/2005- 12/2005
Funded by:

Universitäre Forschungsförderung Charité

Wickens, T.D. (1993). Quantitative methods for estimating the size of a drug-using population. The Journal of Drug Issues 23, 185-216. Zelterman, D. (1988). Robust estimation in truncated discrete distributions with application to capture-recapture experiments. Journal of Statistical Planning and Inference 18, 225-237. Hay, G., Smit, F. (2003). Estimating the number of drug injectors from needle exchange data. Addiction Research and Theory 11, 235-243. Böhning, D.; Schön, D. (2005): Nonparametric maximum likelihood estimation of the population size based on the counting distribution. Journal of the Royal Statistical Society, Series C, Applied Statistics, 54, 1-17 Böhning, D., Suppawattanbodee, B., Kusolvisitkul, W., Viwatwongkasem, C. (2004). Estimating the number of drug users in Bangkok 2001: A capture-recapture approach using repated netries in one list. European Journal of Epidemiology (to appear).