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Sample-size Determination for Analysis of Ecstasy Pills
Linköping University, Faculty of Arts and Sciences. Linköping University, Department of Mathematics, Statistics .
2005 (English)In: The Sixth International Conference on Forensic Statistics, Tempe, AZ, USA, 2005Conference paper (Other academic)
Abstract [en]

By experience, a seizure of pills that is under suspicion to contain drugs will very likely either consist entirely of drug pills of the same kind or consist of pills with no drug-content at all. If this experience could be quantified, it is possible to reduce the number of pills that must be selected for analysis. Recent results show that a Bayesian approach to sample size determination expresses the problem in a more natural way from a forensic point of view, provided an informative prior can be defined. Also, the sample sizes can be further reduced in this framework compared with the more classical Hypergeometric approach. These results have been adopted by the European Network of Forensic Sciences Institutes (ENFSI) in the Guideline on Representative Drug Sampling, published by ENFSI Drug Working Group. In this text, as well as in other published results, it is suggested to use a beta-prior which should be highly left-skewed when assumptions of the above kind can be done. In this paper we show how a beta-prior can be calculated from a data-base of analysed Ecstasy pills. By dividing the data-base items into different sub-populations, it is possible to estimate the parameter in the prior that controls the left-skewness of the distribution.

Place, publisher, year, edition, pages
Keyword [en]
drug sampling, beta-prior, resampling
National Category
URN: urn:nbn:se:liu:diva-29420Local ID: 14764OAI: diva2:250234
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2010-09-28

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