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Correction to Tzidony and Ravreby (1992): A Statistical Approach to Drug Sampling: A Case Study
Author(s) -
Stoel Reinoud D.,
Bolck Annabel
Publication year - 2010
Publication title -
journal of forensic sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.715
H-Index - 96
eISSN - 1556-4029
pISSN - 0022-1198
DOI - 10.1111/j.1556-4029.2009.01256.x
Subject(s) - confidence interval , statistics , sample size determination , sample (material) , sampling (signal processing) , population , standard error , mathematics , computer science , medicine , chromatography , environmental health , chemistry , filter (signal processing) , computer vision
In 1992, Tzidony and Ravreby presented a confidence interval for the total weight of a seizure of illicit drugs present in a population. Their approach has subsequently been applied by several researchers in the field. The formula on which their approach is based does, however, not fully take into account the proportion of drug units found in the sample. In this paper, a modification is presented that consistently uses the correct sample size in all terms of the confidence interval, based on the proportion of drug units found in the sample. The effective sample size is smaller than the original sample size, and this should consequently be accounted for in the estimation of the standard error and in the corresponding t ‐distribution. The new confidence interval is again based on the assumption that the proportion of drug units in the population is known after sampling.