A continuous model for interpreting the positions of bands in DNA locus-specific work.

A simple but rigorous approach is offered for evaluating the evidential value of single locus DNA autoradiographs. This approach does not use a binning technique and it does not treat alleles as discrete variables. Instead, the allele distribution is considered to be continuous. The variation between two comparable bands is assessed using previously determined experimental parameters. The Bayesian treatment leads to an expression of the "quality of a match".     

Experimental design for acquiring relevant data to address the issue of comparing consecutively manufactured tools and firearms

The comparison of consecutively manufactured tools and firearms has provided much, but not all, of the basis for the profession of firearm and toolmark examination. The authors accept the fundamental soundness of this approach but appeal to the experimental community to close two minor gaps in the experimental procedure. We suggest that “blinding” and attention to appropriateness of other experimental conditions that would consolidate the foundations of our profession. We do not suggest that previous work is unsound.     

Dealing with allelic dropout when reporting the evidential value in DNA relatedness analysis

A method is suggested that allows the use of loci that have shown allelic dropout in kinship analysis as used for disaster victim identification (DVI) and missing person work (MP). This approach uses an extension of a previously published approach to modelling allelic dropout. This method may salvage some information in cases where allelic dropout is hindering DVI or MP work particularly in reconciliations involving a large number of bodies and pedigrees. It should not replace the pursuit of more complete DNA profiles by the normal rework process for such samples.     

A comparison of adjustment methods to test the robustness of an STR DNA database comprised of 24 European populations

An aim of the European Network of Forensic Science Institutes (ENFSI) is to produce a DNA database of second generation multiplex (SGM) STR profiles that is representative of the resident cosmopolitan populations. To achieve this, data were collected from 24 different populations. All of the data were combined to form one database of 5700 profiles from which allele proportions were calculated. The robustness of this combined European database was tested by estimating parameter d for every DNA profile, where d=log(10)(Pm(c)/Pm(E)) Pm(c) is the match probability of the profile calculated from its cognate database and Pm(E) is the match probability of the combined European database. Overall there was a small tendency for Pm(c)>Pm(E) primarily because of sampling bias. This bias was removed by the simple expediency of applying an adjustment factor to the calculation of Pm(E). These were selected from the Balding size bias correction, the Balding and Nichols Fst correction, a minimum allele proportion (between 0.01 and 0.02), an upper bound of a 95% confidence interval (CI) and a lower bound on the genotype match probability. It was demonstrated that a single European database is a feasible proposition. A combination of different adjustment methods can be used to ensure that the result is conservative relative to the cognate database, and their effect measured by parameter d.     

The two trace transfer problem re-examined.

The classical two trace transfer problem initially discussed by Evett is reconsidered [Evett IW. On Meaningful Questions: A Two-Trace Transfer Problem. Journal of the Forensic Science Society 1987; 27: 375-381]. In this problem we consider the situation where there are two stains of differing types at a crime scene. Evett considered the situation where both are known to be relevant to the offence. It was further assumed that there were exactly two offenders. Reanalysis of this problem suggests that the key consideration is the conditioning on there being exactly two offenders, not that there were two stains. The treatment here leads easily to a generalisation in which stains have differing relevance and there are k offenders.     

Dealing with allelic dropout when reporting the evidential value in DNA relatedness analysis

A method is suggested that allows the use of loci that have shown allelic dropout in kinship analysis as used for disaster victim identification (DVI) and missing person work (MP). This approach uses an extension of a previously published approach to modelling allelic dropout. This method may salvage some information in cases where allelic dropout is hindering DVI or MP work particularly in reconciliations involving a large number of bodies and pedigrees. It should not replace the pursuit of more complete DNA profiles by the normal rework process for such samples.     

What is the magnitude of the subpopulation effect?

The effect of population subdivision on estimated match probabilities has been raised [Nature 339 (1989) 501; Am. J. Hum. Genet. 48 (1991) 819; Science 254 (1991) 1921]. Previous work [J. Forensic Sci. 39 (1994) 319; J. Forensic Sci. 39 (1994) 988; Am. J. Hum. Genet. 55 (1994) 533] has compared product rule estimates from differing databases and found that the "subpopulation" error may be of the order of a factor of 10. This approach compares an estimate with an estimate. This paper uses simulation to extend these studies by allowing a comparison to a 'true match probability' and supports the conclusion that subpopulation effects are mild. In addition the performance of recommendations 4.1 and 4.2 of NRC II [National Research Council and C.O.D.F. Science, The Evaluation of Forensic DNA Evidence, National Academy Press, Washington, DC, 1996].     

Logical implications of applying the principles of population genetics to the interpretation of DNA profiling evidence

There have been several efforts to codify the approach to interpreting DNA evidence [National Research Council, The Evaluation of Forensic DNA Evidence, National Academy Press, Washington, DC, 1996; I.W. Evett, B.S. Weir, Interpreting DNA Evidence: Statistical Genetics for Forensic Scientists Sinauer, Sunderland, MA, 1998]. Despite these efforts there are still aspects of ad hoc decision making in modern DNA interpretation. This article discusses some of the remaining areas of concern in this respect. Because of the immense discriminating power of DNA evidence it is unlikely that these concerns would contribute to a miscarriage of justice. They are more likely to lead to lengthy and wasteful debate in court, and to potential appeals. We advocate a previously developed approach to DNA evidence [Sci. Justice 39 (4) (1999) 257; B.S. Weir, in: D.J. Balding, C. Cannings, M. Bishop (Eds.), Handbook of Statistical Genetics, Wiley Series in Probability and Statistics, Wiley, New York, ISBN: 0-471-86094-8, 2001; J. R. Stat. Soc. A 158 (1) (1995) 21] that would give a more solid logical foundation and hopefully lead to sounder and less debatable testimony.