| Abstract: | In this paper, a method is described to quantify estimations of the total amount of drugs in groups of seized items, including quantification of the precision. Previous work on this topic was based on the assumptions of normally distributed measurements and grouping of items with a common relative standard deviation. In practice, these assumptions are often violated, for example, for data with point masses at 0, or if certain items in a group have a very high standard deviation. The method described in this paper is based on work by Welch and Satterthwaite and does not assume constant relative standard deviations. Case examples are described for which the method is applied, and simulation studies are carried out for which both methods are applied. In the cases, both methods perform reasonably well. If the assumption of common relative standard deviations clearly does not apply, it is advised to use the method described. |
