Quantifying Uncertainty in Estimations of the Total Weight of Drugs in Groups of Complex Matrices

Abstract

In case practice at forensic drug departments, multiple items from one seizure are sometimes sent in with the question: what is the total amount of drugs in the seizure? This may be complicated especially if impregnated material is involved such as clothes or rubber. Measurement uncertainty is typically stable on drug percentages, not weights, and subsampling may take place. It is recognized more and more that determination and reporting of uncertainty on estimators are an essential part of obtaining scientifically sound results in the forensic field. Methodology is described to quantify uncertainty on estimations of the total drug weight in groups of complex matrices, given simple statistical models, along a subdivision of five types of cases. Given each of these types, case examples are given where uncertainty is quantified in estimations of drug weights, by means of confidence intervals. The described models are statistically sound and relatively easy to implement.