Forensic Science South Australia

Adelaide, Australia

Forensic Science South Australia

Adelaide, Australia
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News Article | May 17, 2017
Site: www.prweb.com

The Federal Bureau of Investigation (FBI) has published its validation of STRmix™ for use on mixtures of up to five persons, as well as across a wide range of templates and mixture ratios. The FBI began use of STRmix in casework in December 2015. This publication details the extensive validation work done by the FBI to underpin that casework use. The findings show that STRmix™ – a sophisticated forensic software used by trained, experienced DNA experts to resolve mixed DNA profiles previously thought unresolvable – is sufficiently robust for implementation in forensic laboratories. The FBI’s internal validation, published in FSI: Genetics, notes that STRmix™ offers numerous advantages over historical methods of DNA profile analysis and has greater statistical power for estimating evidentiary weight, all of which can be used reliably in human identification testing. “The validation largely meets the requirements of the President’s Council of Advisors on Science and Technology (PCAST) for the foundational validity of STRmix™ for one-to-five person mixtures at a wide range of ratio and template,” explains Dr. John Buckleton, DSc, FRSNZ, Forensic Scientist at the New Zealand Institute of Environmental Science and Research (ESR). Buckleton and fellow ESR scientist Jo-Anne Bright, in collaboration with Duncan Taylor from Forensic Science South Australia (FSSA), developed STRmix™. Using standard, well-established statistical methods, STRmix™ builds up a picture of the DNA genotypes that, when added together, best explains the observed mixed DNA profile. STRmix™ then enables users to compare the results against a person or persons of interest and calculate a statistic, or “likelihood ratio,” of the strength of the match. Studies to assess and internally validate STRmix™ for casework use at the FBI were conducted using lab-specific parameters and more than 300 single-source and mixed contributor profiles. Simulated forensic specimens, including constructed mixtures that incorporated DNA from two-to-five donors across a broad range of template amounts and contributor proportions, were used to examine the sensitivity and specificity of the system via more than 60,000 tests that compared hundreds of known contributors and non-contributors to the specimens. Conditioned analyses, concurrent interpretation of amplification replicates, and application of an incorrect contributor number were also performed to further investigate software performance and probe the limitations of the system. In addition, the results from manual and probabilistic interpretation of both prepared and evidentiary mixtures were compared. Eighteen labs in the U.S. are now using STRmix™, while another 55 U.S. labs are at various stages of installation, validation, and training. In addition, STRmix™ is being used by numerous local, state, and federal agencies, including the U.S. Army Criminal Investigation Laboratory (USACIL) and the California Department of Justice. To date, there have been at least seven successful admissibility hearings for STRmix™ in the U.S., while DNA evidence interpreted with STRmix™ has been successfully used in more than 65 other court cases. Internationally, STRmix™ has been used in casework since 2012, and has been used to interpret DNA evidence in thousands of cases. It is currently in use in labs in Australia, New Zealand, England, Scotland, Ireland, and Canada. For more information about STRmix™ visit http://www.esr.cri.nz/ or http://strmix.esr.cri.nz/.


Bright J.-A.,Institute of Environmental Science and Research Ltd | Bright J.-A.,University of Auckland | Taylor D.,Forensic Science South Australia | Curran J.,University of Auckland | Buckleton J.,Institute of Environmental Science and Research Ltd
Forensic Science International: Genetics | Year: 2014

DNA databases have revolutionised forensic science. They are a powerful investigative tool as they have the potential to identify persons of interest in criminal investigations. Routinely, a DNA profile generated from a crime sample could only be searched for in a database of individuals if the stain was from single contributor (single source) or if a contributor could unambiguously be determined from a mixed DNA profile. This meant that a significant number of samples were unsuitable for database searching. The advent of continuous methods for the interpretation of DNA profiles offers an advanced way to draw inferential power from the considerable investment made in DNA databases. Using these methods, each profile on the database may be considered a possible contributor to a mixture and a likelihood ratio (LR) can be formed. Those profiles which produce a sufficiently large LR can serve as an investigative lead. In this paper empirical studies are described to determine what constitutes a large LR. We investigate the effect on a database search of complex mixed DNA profiles with contributors in equal proportions with dropout as a consideration, and also the effect of an incorrect assignment of the number of contributors to a profile. In addition, we give, as a demonstration of the method, the results using two crime samples that were previously unsuitable for database comparison. We show that effective management of the selection of samples for searching and the interpretation of the output can be highly informative. © 2013 Elsevier Ireland Ltd.


Taylor D.,Forensic Science South Australia | Taylor D.,Flinders University | Buckleton J.,ESR
Forensic Science International: Genetics | Year: 2015

A set of low template mixed DNA profiles with known ground truths was examined using software that utilised peak heights (STRmix™ V2.3) and an adapted version that did not use peak heights and mimicked models based on a drop-out probability [1,2] (known as semi-continuous or 'drop' models) (STRmix™ lite). The use of peak heights increased the LR when Hp was true in the vast majority of cases. The effect was most notable at moderate template levels but was also present at quite low template levels. There is no level at which we can say that height information is totally uninformative. Even at the lowest levels the bulk of the data show some improvement from the inclusion of peak height information. © 2014 Elsevier Ireland Ltd. All rights reserved.


Taylor D.,Forensic Science South Australia | Bright J.-A.,ESR Ltd | Buckleton J.,ESR Ltd
Forensic Science International: Genetics | Year: 2013

A method for interpreting autosomal mixed DNA profiles based on continuous modelling of peak heights is described. MCMC is applied with a model for allelic and stutter heights to produce a probability for the data given a specified genotype combination. The theory extends to handle any number of contributors and replicates, although practical implementation limits analyses to four contributors. The probability of the peak data given a genotype combination has proven to be a highly intuitive probability that may be assessed subjectively by experienced caseworkers. Whilst caseworkers will not assess the probabilities per se, they can broadly judge genotypes that fit the observed data well, and those that fit relatively less well. These probabilities are used when calculating a subsequent likelihood ratio. The method has been trialled on a number of mixed DNA profiles constructed from known contributors. The results have been assessed against a binary approach and also compared with the subjective judgement of an analyst. © 2013 Elsevier Ireland Ltd. All rights reserved.


Stephan C.N.,POW Inc | Stephan C.N.,University of Queensland | Simpson E.K.,Forensic Science South Australia | Byrd J.E.,POW Inc
Journal of Forensic Sciences | Year: 2013

Several methods that have customarily been used in craniofacial identification to describe facial soft tissue depths (FSTDs) implore improvement. They include the calculation of arithmetic means for skewed data, omission of concern for measurement uncertainty, oversight of effect size, and misuse of statistical significance tests (e.g., p-values for strength of association). This paper redresses these limitations using FSTDs from 10 prior studies (N = 516). Measurement uncertainty was large (>20% of the FSTD), skewness (≥0.8) existed at 11 of the 23 FSTD landmarks examined, and sex and age each explained <4% of the total FSTD variance (η2 calculated as part of MANOVA). These results call for a new and improved conceptualization of FSTDs, which is attained by the replacement of arithmetic means with shorths and 75-shormaxes. The outcomes of this implementation are dramatic reduction in FSTD complexity; improved data accuracy; and new data-driven standards for casework application of methods. © 2013 American Academy of Forensic Sciences.


Taylor D.,Forensic Science South Australia | Bright J.-A.,ESR Ltd | Buckleton J.,ESR Ltd | Curran J.,University of Auckland
Forensic Science International: Genetics | Year: 2014

A typical assessment of the strength of forensic DNA evidence is based on a population genetic model and estimated allele frequencies determined from a population database. Some experts provide a confidence or credible interval which takes into account the sampling variation inherent in deriving these estimates from only a sample of a total population. This interval is given in conjunction with the statistic of interest, be it a likelihood ratio (LR), match probability, or cumulative probability of inclusion. Bayesian methods of addressing database sampling variation produce a distribution for the statistic from which the bound(s) of the desired interval can be determined. Population database sampling uncertainty represents only one of the sources of uncertainty that affects estimation of the strength of DNA evidence. There are other uncertainties which can potentially have a much larger effect on the statistic such as, those inherent in the value of Fst, the weights given to genotype combinations in a continuous interpretation model, and the composition of the relevant population. In this paper we model the effect of each of these sources of uncertainty on a likelihood ratio (LR) calculation and demonstrate how changes in the distribution of these parameters affect the reported value. In addition, we illustrate the impact the different approaches of accounting for sampling uncertainties has on the LR for a four person mixture.


Taylor D.A.,Forensic Science South Australia | Henry J.M.,Forensic Science South Australia
Forensic Science International: Genetics | Year: 2012

Y-STR haplotype data was obtained using the AmpFlSTR® YFiler™ PCR Amplification Kit (Applied Biosystems, Foster City, CA) for 1079 Caucasian and 766 Australian Aboriginal individuals. Haplotype diversity was similar in both populations, however discrimination capacity was higher in Caucasians than Aborigines (0.946 compared to 0.692). Locus DYS385, which was considered as a single locus, was the most diverse marker in both populations (0.836 in Caucasians and 0.905 in Aborigines). Population: The South Australian Aboriginal and Caucasian databases were compiled from casework reference profile information held on the South Australian Criminal, Reference and Evidence DNA Database (SACREDD). Ethnicity was assigned based on self-declaration. © 2012 Published by Elsevier Ireland Ltd. All rights reserved.


Bright J.-A.,ESR Ltd | Bright J.-A.,University of Auckland | Taylor D.,Forensic Science South Australia | Curran J.M.,University of Auckland | Buckleton J.S.,ESR Ltd
Forensic Science International: Genetics | Year: 2013

Traditional forensic DNA interpretation methods are restricted as they are unable to deal completely with complex low level or mixed DNA profiles. This type of data has become more prevalent as DNA typing technologies become more sensitive. In addition they do not make full use of the information available in peak heights. Existing methods of interpretation are often described as binary which describes the fact that the probability of the evidence is assigned as 0 or 1 (hence binary) (see for example [1] at 7.3.3). These methods are being replaced by more advanced interpretation methods such as continuous models. In this paper we describe a series of models that can be used to calculate expected values for allele and stutter peak heights, and their ratio SR. This model could inform methods which implement a continuous method for the interpretation of DNA profiling data. © 2013 Elsevier Ireland Ltd.


Ottens R.,Flinders University | Taylor D.,Forensic Science South Australia | Abarno D.,Forensic Science South Australia | Linacre A.,Flinders University
Forensic Science, Medicine, and Pathology | Year: 2013

We report on successful amplification of DNA profiles from a single hair. Direct amplification was used on the root tip of both anagen and telogen hairs using a kit to amplify 15 STR loci. All 30 anagen hairs tested from five different people gave full DNA profiles after 29 cycles with no allelic drop-in or heterozygous imbalance. Six of the 30 telogen hairs tested resulted in a full DNA profile, and a further four telogen hair samples tested produced a DNA profile of five or more complete loci that could be up-loaded to the National DNA Database (Australia). A full DNA profile was also obtained from the shaft of an anagen hair. Current practice for many laboratories is that a single hair may not be subjected to DNA testing as there is little chance of success, hence this 100 % success rate from anagen hairs is a significant advancement. A full DNA profile was obtained from a 5 year-old single hair illustrating the success when using direct PCR rather than attempting an extraction prior to the amplification step. The process described deliberately uses current DNA profiling methods with no increase in cycle number, such that the methodology can be incorporated readily into operational practice. For the first time in the field of human identification, single hairs can be analyzed with confidence that a meaningful DNA profile will be generated and the data accepted by the criminal justice system. © 2012 Springer Science+Business Media New York.


Taylor D.,Forensic Science South Australia | Taylor D.,Flinders University
Forensic Science International: Genetics | Year: 2014

Continuous DNA interpretation systems make use of more information from DNA profiles than analysts have previously been able to with binary, threshold based systems. With these new continuous DNA interpretation systems and a new, more powerful, DNA profiling kit (GlobalFiler) there is an opportunity to re-examine the behaviour of a commonly used statistic in forensic science, the likelihood ratio (LR). The theoretical behaviour of the LR has been known for some time, although in many instances the behaviour has not been able to be thoroughly demonstrated due to limitations of the biological and mathematical models being used. In this paper the effects of profile complexity, replicate amplifications, assuming contributors, adding incorrect information, and adding irrelevant information to the calculation of the LR are explored. The empirical results are compared to theoretical expectations and explained. The work finishes with the results being used to dispel common misconceptions around reliability, accuracy, informativeness and reproducibility. © 2014 Published by Elsevier Ireland Ltd. All rights reserved.

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