Analysis of DNA multilocus profiles in a paternity case in which the child's profile may be partial

This report describes a simple approach to multilocus paternity analysis for cases where the child's sample may be inadequate leading to a partial profile. A specimen calculation is given. A previous paper described how the various band sharing configurations in the DNA multilocus profiles of a mother-child-putative father trio could be combined in a comprehensive mathematical analysis to give an overall Bayesian likelihood ratio. In that paper, it was assumed that all three members of the trio gave full DNA profiles. In some cases that assumption may not be valid but it is possible to extend the analysis to allow for partial profiles. This paper demonstrates how this may be done by considering the case where the child's profile may be partial for one reason or another. A specimen calculation is given.     

A guide to interpreting single locus profiles of DNA mixtures in forensic cases.

Analysis of a mixed body fluid crime sample by means of a single locus DNA probe may give rise to several bands. If a suspect is found to have a profile which matches two of the bands, then the evaluation of the evidential strength requires careful analysis. This paper describes the analysis of two relatively simple case examples. It is intended that the principles of the interpretative process will provide a guide to caseworkers who may encounter similar cases. The extension of the treatment to more complex cases should be clear.     

The interpretation of refractive index measurements. III

The question of whether or not to group recovered glass fragments before comparison with a control sample is fundamental to the interpretation of refractive index measurements. A computer program has been written to perform the grouping and explore the consequences. Grouping the fragments is shown to increase the chances of finding all recovered fragments similar when they have in fact come from the same source as the control, and to give enhanced discrimination when the recovered glass has come from a different source. When the recovered fragments have come from two different sources the consequences of the grouping procedure are preferable to non-grouping.     

Interpreting small quantities of DNA: the hierarchy of propositions and the use of Bayesian networks

The dramatic increase in the sensitivity of DNA profiling systems that has occurred over recent years has led to the need to address a wider range of interpretational problems in forensic science. The issues surrounding questions of the kind "whose DNA is this?" have been the subject of considerable controversy but now it is clear that the emphasis is shifting to questions of the kind "how did this DNA get here?" Such issues are discussed in this paper and new insights are provided by two particular recent developments. First, the notion of the "hierarchy of propositions" that has arisen from a project called Case Assessment and Interpretation (CAI) that has been running in the British Forensic Science Service (FSS). Second, a technique for drawing inferences in the face of many interacting considerations, known as "Bayesian networks"--or "Bayes' nets" for short--that has been the subject of an earlier paper in this journal (1). The discussion is carried out by means of case studies, based on actual cases. It is clear that, whereas the inference in relation to the source of the DNA in a crime sample might be overwhelmingly strong, the inference in relation to the propositions that a jury must consider relating to the identity of the actual offender may be much more tentative.     

The nature of forensic science opinion--a possible framework to guide thinking and practice in investigations and in court proceedings.

The questions that are asked of forensic scientists during the course of a criminal investigation, and during subsequent court proceedings, are of varied form. This paper attempts to place these questions into broad generic types and explores the difference in the inferential process that a scientist may employ when forming opinions that help answer these questions. From this model, a working definition of different roles and attributes for forensic scientists is described which may offer greater clarity for both practitioners and users of forensic science.     

The interpretation of refractive index measurements. II

The method for interpreting refractive index measurements described previously in this journal (Forensic Sci., 9 (1977) 209 – 217) is generalised. The assumption that the variance of within-window variation is the same for all windows is replaced by a less restrictive assumption which is based on standard deviation estimates collected in the course of routine casework.     

Earmarks as evidence: a critical review.

The use of earmarks as evidence in criminal trials appears to be expanding, but there is something of a dearth of peer-reviewed scientific publications to support the pursuit. This paper is a critical review of the current literature in which we emphasize the weaknesses of the present state of knowledge. Some research directions are proposed to gather statistical knowledge of the within-source and between-source variability of earmarks and earprints. Its ultimate goal is to be able to assess likelihood ratios in relation to this type of evidence.