Duncan Taylor

Duncan Taylor
Forensic Science South Australia · Department of Biology

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160
Publications
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Publications

Publications (160)
Preprint
Full-text available
We discuss a range of miscodes found in probabilistic genotyping (PG) software and from other industries that have been reported in the literature and have been used to inform PG admissibility hearings. Every instance of the discovery of a miscode in PG software with which we have been associated has occurred either because of testing, use, or repe...
Article
Full-text available
The sensitivity and discrimination power of modern DNA profiling systems means that very small amounts of DNA from an individual can be detected on an item leading to large inclusionary statistics for that person. The sensitivity of these systems has significant benefits in the investigation of crime but also can be highly sensitive to contaminatio...
Article
The interpretation of mixtures containing related individuals can be difficult due to allele sharing between the contributors. Challenges include the assignment of the number of contributors (NoC) to the mixture with the under assignment of NoC resulting in false exclusions of true donors. Non-donating relatives of the true contributors to mixtures...
Article
ABTRACT Rapid DNA instruments are gaining interest in the forensic community as a means to generate DNA profile information more quickly than standard laboratory workflows, and with the potential to be carried out at the scene where samples are taken. Due to the many years that DNA profiles have been generated in a standard laboratory workflow, the...
Article
Current forensic DNA profiling kits and techniques enable the detection of trace amounts of DNA. With advancements in kit sensitivity, there is an increased probability of detecting DNA from contamination. Research into DNA transfer within operational forensic laboratories provides insight into the possible mechanisms that may lead to exhibit conta...
Article
Although a version of direct PCR is implemented in forensic laboratories for reference material, its incorporation into workflow for the analysis of touch DNA, as a form of latent DNA, from casework exhibits is not. In addition to concerns about increased sensitivity causing more complex mixtures or the generation of more genetic data implicating a...
Article
With an increase in the application of direct PCR to items of forensic relevance, as well as the array of STR kits available for amplification, the need for a comprehensive investigation into the optimum STR panel for this workflow has arisen. Here we examine the relative STR amplification success of touch DNA on a range of substrates, with surface...
Article
Abtract Forensic Science South Australia (FSSA) has been using STRmix™ software to deconvolute all reported DNA mixtures since 2012. Almost a decade of deconvolutions had led to a substantial repository of analysed profile data that can be interrogated to observe trends in case type, location or occurrence. In addition, deconvolutions can be compar...
Article
DNA profiles are generated in forensic biology laboratories around the world. It is possible that these profiles are assessed by two independent people in order for the profiles to be ‘read’. Recent work has been carried out to develop a neural network model to classify fluorescence in a DNA profile electropherogram and potentially replace one, or...
Article
Full-text available
Probabilistic genotyping has become widespread. EuroForMix and DNAStatistX are both based upon maximum likelihood estimation using a γ model, whereas STRmix™ is a Bayesian approach that specifies prior distributions on the unknown model parameters. A general overview is provided of the historical development of probabilistic genotyping. Some genera...
Article
A typical forensic laboratory process for interpreting STR capillary electrophoresis profile data is for two people to independently ‘read’ the profiles, compare results, and resolve any differences. Recently, work has been conducted to develop a machine learning tool called an artificial neural network (ANN) to carry out the same function as a hum...
Article
Likelihood ratios (LR) differences between the probabilistic genotyping software EuroForMix and STRmix™ are examined. After considering differences in the allele probabilities, the LRs from both software for an unambiguous single‐source profile were identical (four significant figures). LRs from both software for an unambiguous single‐source profil...
Article
Cold case reinvestigations are a common occurrence. Occasionally some of the original work was conducted up to 30 years ago using profiling systems of the early 1990s, which targeted HLA-DQA1, ApoB, D1S80 and D17S5. When contemporary work is carried out, if a suspect is identified they will be profiled in contemporary profiling kits such as GlobalF...
Article
ABTRACT Due to advances in DNA profiling sensitivity as well as the implementation of various types of software to analyse these profiles, forensic biologists can provide opinions about results generated from very low levels of template DNA. The ability to obtain DNA profiles from such ‘trace’ DNA brings into question the mechanisms of transfer whi...
Preprint
Full-text available
Two methods for applying a lower bound to the variation induced by the Monte Carlo effect are trialled. One of these is implemented in the widely used probabilistic genotyping system, STRmix ™ . Neither approach is giving the desired 99% coverage. In some cases the coverage is much lower than the desired 99%. The discrepancy (i.e. the distance betw...
Preprint
Full-text available
In previously reported work a method for applying a lower bound to the variation induced by the Monte Carlo effect was trialled. This is implemented in the widely used probabilistic genotyping system, STRmix ™ . The approach did not give the desired 99% coverage. However, the method for assigning the lower bound to the MCMC variability is only one...
Article
Forensic DNA profiling is used in various circumstances to evaluate support for two competing propositions with the assignment of a likelihood ratio. Many software implementations exist that tackle a range of inference problems spanning identification and relationship testing. We propose a flexible likelihood ratio framework that caters to inferenc...
Article
Evaluating forensic biological evidence considering activity level propositions is becoming more prominent around the world. In such evaluations it is common to combine results from multiple items associated with the alleged activities. The results from these items may not be conditionally independent, depending on the mechanism of cell/DNA transfe...
Article
Full-text available
Through advances in fluorescent nucleic acid dye staining and visualisation, targeted collection of cellular material deposited, for example by touch or within a saliva deposit, is possible. In regard to the potential evidentiary value of the deposit the questions remain: ‘How many cells are required to generate an informative DNA profile?’; ‘How m...
Article
Full-text available
A wide variety of items are submitted as evidence in a forensic investigation. Identifying the location of DNA on such items is central to maximizing DNA profiling success and thus the ability to link a person of interest to a particular item or crime. Recent publications describe a fluorescent staining method using Diamond™ Dye (DD) to visualize c...
Article
Slooten described a method of targeting major contributors in mixed DNA profiles and comparing them to individuals on a DNA database. The method worked by taking incrementally more peak information from the profile (based on the peak contribution), and using a semi-continuous model, calculating likelihood ratios for the comparison to database indiv...
Article
Full-text available
In casework, laboratories may be asked to compare DNA mixtures to multiple persons of interest (POI). Guidelines on forensic DNA mixture interpretation recommend that analysts consider several pairs of propositions; however, it is unclear if several likelihood ratios (LRs) per person should be reported or not. The propositions communicated to the c...
Article
We describe a method to assign weights to genotype combinations at the Amelogenin locus. It is a typical practise in forensic laboratories that once the weight exceeds a threshold (such as 99%), then they can be considered to be resolve enough to interpret (for example to load onto a database). We found that unless an individual is a clear major (o...
Article
The assignment of the number of contributors (N) to a forensic DNA profile is undertaken as part of the interpretation process. There is no requirement for N to be the same for both propositions within the likelihood ratio framework. ISFG recommendations on mixture interpretation suggest that there may be times where prosecution and defence both sp...
Article
We seek to develop a rational approach to forming propositions when little information is available from the outset, as this often happens in casework. If propositions used when evaluating evidence are not exhaustive (in the context of the case), then there is a theoretical risk that an LR greater than one may be associated with a proposition in th...
Article
DNA mixtures will have multiple donors under both the prosecution and alternate propositions when assigning a likelihood ratio for forensic DNA evidence. These donors are usually assumed to be unrelated to each other. In this paper, we make a small, preliminary examination of the potential effect of relaxing this assumption. We consider the simple...
Article
We reprise four significant software failures and examine these cases for lessons that can be transferred to the development of forensic software. All four case studies have been well examined and causes described. No one factor is common to all four case studies. The studies are the MIT Kerberos security software, the Mars Climate Orbiter (MCO), t...
Article
In casework there are often multiple mixed DNA profiles with a single unknown offender who is believed to be a contributor. Sometimes none of these profiles are individually informative enough to evaluate whether a person of interest (PoI) is a contributor. We propose a method that combines evidence across multiple mixtures to better resolve the ge...
Article
To answer the question “Are low likelihood ratios reliable?” requires both a definition of reliable and then a test of whether low likelihood ratios (LRs) meet that definition. We offer, from a purely statistical standpoint, that reliability can be determined by assessing whether the expected rate of inclusionary support for non-donors over many ca...
Article
Uncertainty in the assignment of the number of contributors (NoC) can be encountered, particularly in higher-order mixtures, where alleles may be shared between contributors, may have dropped out, or may be masked by the stutter artefacts or allelic peaks of a more dominant contributor. Most probabilistic genotyping software requires the assignment...
Article
As legal practitioners and courts become more aware of scientific methods and evidence evaluation, they are demanding measures of the reliability of expert opinion. In particular, there are calls for error rates to accompany opinion evidence in comparative forensic sciences. While error rates or confidence intervals can be useful for those discipli...
Article
Forensic genetic laboratories perform a large amount of STR analyses of the Y chromosome, in particular to analyze the male part of complex DNA mixtures. However, the statistical interpretation of evidence retrieved from Y-STR haplotypes is challenging. Due to the uni-parental inheritance mode, Y-STR loci are connected to each other and thus haplot...
Article
Full-text available
This paper presents a methodology allowing identification of the variables associated with transfer, persistence or recovery of DNA traces that have the most significant impact on the result of an evaluation measured through a likelihood ratio (LR). It builds on a case scenario involving trace DNA recovered from knife handles where the prosecution...
Article
Sexual assault cases are regularly encountered in forensic laboratories. The victim’s underwear and other clothes are often submitted with the intention of retrieving the offender’s DNA. We examined six sexual assault scenarios; removing underwear, removing brassiere, digital penetration of the vagina from the front, grabbing breasts over the top o...
Article
Stiffelman [1] gives a broad critique of the application of likelihood ratios (LRs) in forensic science, in particular their use in probabilistic genotyping (PG) software. These are discussed in this review. LRs do not infringe on the ultimate issue. The Bayesian paradigm clearly separates the role of the scientist from that of the decision makers...
Article
Improvised explosive devices (IEDs) present a number of challenges in terms of the generation of forensically relevant information. Inhibition to PCR from sub-optimal sample types as well as from specific substrates has historically meant that extraction prior to PCR has been required. Improvements to STR kit buffers lead to the successful introduc...
Article
It is routinely assumed when interpreting forensic DNA profiles that peaks of the same molecular size, whether allelic or stutter in origin, ‘stack’. That is, the height of a composite peak is approximately equal to the sum of its parts. There is strong theoretical reason to believe that this assumption should hold across the range of peak heights...
Article
The advent of DNA profiling in the 1980s has revolutionised forensic science. Forensic DNA profiling is a powerful tool that is used to both exonerate and implicate persons of interest in criminal cases. The technologies used to recover and detect DNA from crime scene stains have evolved over time. Whereas 30 years ago most forensic profiles were g...
Article
In this short publication we address the topic of evaluation of biological results given activity level propositions, particularly when the source of the biological material is not in question. When the issue regards the mechanisms or actions that led to the deposition of the biological material concerned, there is a need for more case information...
Article
Full-text available
The value of the evidence depends critically on propositions. In the second of two papers intended to provide advice to the community on difficult aspects of evaluation and the formulation of propositions, we focus primarily on activity level propositions. This helps the court address the question of "How did an individual's cell material get there...
Article
Peaks in an electropherogram could represent alleles, stutter product, or a combination of allele and stutter. Continuous probabilistic genotyping (PG) systems model the heights of peaks in an additive manner: for a shared or composite peak, PG models assume that the peak height is the sum of the allelic component and the stutter component. In this...
Article
Until recently, forensic DNA profile interpretation was predominantly a manual, time‐consuming process undertaken by analysts using heuristics to determine those genotype combinations that could reasonably explain a recovered profile. Probabilistic genotyping (PG) has now become commonplace in the interpretation of DNA profiling evidence. As the co...
Article
We investigate the ability of the 31 SNP loci in the Global AIMs Nano set to distinguish self-declared Australian Aboriginal individuals from European, Oceanic, African, Native American and East Asian populations. Human evolution suggests that Australian Aboriginal individuals came to Australia approximately 50 000 years ago, during the time it mad...
Article
Trace DNA and the manner in which it is transferred from item to item is a common topic arising in forensic science, both in case evaluations, and in Court testimony. In order to assign the probability of obtaining DNA findings, given competing propositions that specify transfer mechanisms, consideration must be given to a number of factors. Previo...
Article
An intra and inter-laboratory study using the probabilistic genotyping (PG) software STRmix™ is reported. Two complex mixtures from the PROVEDIt set, analysed on an Applied Biosystems™ 3500 Series Genetic Analyzer, were selected. 174 participants responded. For Sample 1 (low template, in the order of 200 rfu for major contributors) five participant...
Article
Standard practice in forensic science is to compare a person of interest's (POI) reference DNA profile with an evidence DNA profile and calculate a likelihood ratio that considers propositions including and excluding the POI as a DNA donor. A method has recently been published that provides the ability to compare two evidence profiles (of any numbe...
Article
Evaluative reporting provides a balanced approach to evidence interpretation. The use of evaluative reporting in forensic DNA analysis is common practice and well understood in Australia and New Zealand. However, it is less common and perhaps less understood in the pattern and trace evidence areas. Recent publications, such as the 2015 ‘European Ne...
Article
A recent publication has provided the ability to compare two mixed DNA profiles and consider their probability of occurrence if they do, compared to if they do not, have a common contributor. This ability has applications to both quality assurance (to test for sample to sample contamination) and for intelligence gathering purposes (did the same unk...
Article
Familial Searching has been used in numerous jurisdictions globally since the turn of the century and has provided successful investigative leads and prosecutions. We present a familial search performed at Forensic Science SA in conjunction with the South Australian Police that resulted in an intelligence lead, arrest and conviction of an individua...
Article
Full-text available
The hierarchy of propositions has been accepted amongst the forensic science community for some time. It is also accepted that the higher up the hierarchy the propositions are, against which the scientist are competent to evaluate their results, the more directly useful the testimony will be to the court. Because each case represents a unique set o...
Article
Previous work has shown that artificial neural networks can be used to classify signal in an electropherogram into categories that have interpretational meaning (such as allele, baseline, pull-up or stutter). The previous work trained the neural networks on a single data type, produced under a single laboratory condition and applied it to data that...
Article
Using a simplified model, we examine the effect of varying the number of contributors in the prosecution and alternate propositions for a number of simulated examples. We compare the Slooten and Caliebe [1] solution, with several existing practices. Our own experience is that most laboratories, and ourselves, assign the number of contributors, N =...
Book
Now in its second edition, Forensic DNA Evidence Interpretation is the most comprehensive resource for DNA casework available today. Written by leaders in the fields of biology and statistics, including a contribution from Peter Gill, the father of DNA analysis, the book emphasizes the interpretation of test results and provides the necessary formu...
Article
Forensic DNA interpretation is transitioning from manual interpretation based usually on binary decision‐making toward computer‐based systems that model the probability of the profile given different explanations for it, termed probabilistic genotyping (PG). Decision‐making by laboratories to implement probability‐based interpretation should be bas...
Article
The interpretation of evidence continues to be one of the biggest challenges facing the forensic community. This is the first of two papers intended to provide advice on difficult aspects of evaluation and in particular on the formulation of propositions. The scientist has a dual role: investigator (crime-focused), where often there is no suspect a...
Article
Many methods have been suggested for evaluating the evidential value of a matching Y-chromosomal DNA profile obtained from a biological stain associated with a crime scene and the Y-chromosomal DNA profile of a suspect. Most of these methods are based on estimating the population frequency of the Y-profile. The common independence assumption betwee...
Article
Full-text available
The evaluation of results of forensic genetic analyses given activity level propositions is an emerging discipline in forensic genetics. Although it is a topic with a long history, it has never been considered to be such a critically important topic for the field, as today. With the increasing sensitivity of analysis techniques, and advances in dat...
Article
Direct PCR from touch DNA has a range of potential applications in the field of forensic investigation for exhibit examination that, under standard extraction methods, rarely produce informative DNA profiles. Previous studies from 'touch DNA' have focussed on fingermarks created under laboratory conditions. Here we report on successful STR DNA prof...
Article
Full-text available
Recently, Lund and Iyer (L&I) raised an argument regarding the use of likelihood ratios in court. In our view, their argument is based on a lack of understanding of the paradigm. L&I argue that the decision maker should not accept the expert's likelihood ratio without further consideration. This is agreed by all parties. In normal practice, there i...
Article
In this paper we introduce a new likelihood ratio method for evaluating mixed Y-STR profiles that is based on the premise that, given a haplotype has been seen in the person of interest, the most likely source of a second haplotype, matching at all or most loci, is in an individual with a recent common ancestor. We have called the new method the “H...
Article
STRmix™ uses several laboratory specific parameters to calibrate the stochastic model for peak heights. These are modelled on empirical observations specific to the instruments and protocol used in the analysis. The extent to which these parameters can be borrowed from laboratories with similar technology and protocols without affecting the accurac...
Article
Modern probabilistic genotyping (PG) software is capable of modeling stutter as part of the profile weighting statistic. This allows for peaks in stutter positions to be considered as allelic or stutter or both. However, prior to running any sample through a PG calculator, the examiner must first interpret the sample, considering such things as art...
Article
We report a large compilation of the internal validations of the probabilistic genotyping software STRmix™. Thirty one laboratories contributed data resulting in 2825 mixtures comprising three to six donors and a wide range of multiplex, equipment, mixture proportions and templates. Previously reported trends in the LR were confirmed including less...
Article
Full-text available
We present here the derivation of paternity index formulae that covers situations of a disputed paternity trio with a trisomic product of conception. We consider six possible mechanisms for trisomy to occur: dispermy, dieggy, paternal meiosis I or II, and maternal meiosis I or II in the calculation. We also provide a biological explanation for how...