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Evaluation of the Likelihood Ratio for Fibre Transfer Evidence in Criminal Cases
Author(s) -
Evett I. W.,
Cage P. E.,
Aitken C. G. G.
Publication year - 1987
Publication title -
journal of the royal statistical society: series c (applied statistics)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.205
H-Index - 72
eISSN - 1467-9876
pISSN - 0035-9254
DOI - 10.2307/2347549
Subject(s) - statistics , mathematics , psychology , econometrics
SUMMARY During the commission of a crime, particularly a violent crime, it is possible that fibres may be transferred: perhaps from criminal to victim, or from victim to criminal. Recently, new methods have been introduced which enable quantitative colour measurements to be made on individual fibres and a data collection of colour measurements on a sample of 8000 fibres has been built up. A method is described for evaluating the likelihood ratio for the case in which a single fibre has been left at the scene of a crime and it is to be compared with a sample of fibres of known origin (the control). The numerator of the likelihood ratio is based on the hypothesis that the single fibre came from the same source as the control and is evaluated by means of a predictive distribution. The denominator is based on the hypothesis that the single fibre came from some other source in the population of fibre sources. The sample is assumed to be representative of that population and is used, through kernel density estimation, to evaluate the denominator which is essentially a measure of how rare or common the particular fibre colour is. An experiment based on wool samples in the collection is described.