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Statistical analysis tools of mixture DNA samples: When the same software provides different results. FORENSIC SCIENCE INTERNATIONAL GENETICS SUPPLEMENT SERIES 2022. [DOI: 10.1016/j.fsigss.2022.09.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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2
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Quantification of forensic genetic evidence: Comparison of results obtained by qualitative and quantitative software for real casework samples. Forensic Sci Int Genet 2022; 59:102715. [DOI: 10.1016/j.fsigen.2022.102715] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 03/29/2022] [Accepted: 04/21/2022] [Indexed: 11/22/2022]
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3
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Manabe S, Fukagawa T, Fujii K, Mizuno N, Sekiguchi K, Akane A, Tamaki K. Development and validation of Kongoh ver. 3.0.1: Open-source software for DNA mixture interpretation in the GlobalFiler system based on a quantitative continuous model. Leg Med (Tokyo) 2021; 54:101972. [PMID: 34629243 DOI: 10.1016/j.legalmed.2021.101972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/27/2021] [Accepted: 09/28/2021] [Indexed: 10/20/2022]
Abstract
Probabilistic genotyping software based on continuous models is effective for interpreting DNA profiles derived from DNA mixtures and small DNA samples. In this study, we updated our previously developed Kongoh software (to ver. 3.0.1) to interpret DNA profiles typed using the GlobalFiler™ PCR Amplification Kit. Recently, highly sensitive typing systems such as the GlobalFiler system have facilitated the detection of forward, double-back, and minus 2-nt stutters; therefore, we implemented statistical models for these stutters in Kongoh. In addition, we validated the new version of Kongoh using 2-4-person mixtures and DNA profiles with degradation in the GlobalFiler system. The likelihood ratios (LRs) for true contributors and non-contributors were well separated as the information increased (i.e., larger peak height and fewer contributors), and these LRs tended to neutrality as the information decreased. These trends were observed even in profiles with DNA degradation. The LR values were highly reproducible, and the accuracy of the calculation was also confirmed. Therefore, Kongoh ver. 3.0.1 is useful for interpreting DNA mixtures and degraded DNA samples in the GlobalFiler system.
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Affiliation(s)
- Sho Manabe
- Department of Legal Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan.
| | - Takashi Fukagawa
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Koji Fujii
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Natsuko Mizuno
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Kazumasa Sekiguchi
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Atsushi Akane
- Department of Legal Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Keiji Tamaki
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
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Interpretation of DNA data within the context of UK forensic science - evaluation. Emerg Top Life Sci 2021; 5:405-413. [PMID: 34027985 PMCID: PMC8760892 DOI: 10.1042/etls20200340] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Revised: 04/24/2021] [Accepted: 05/04/2021] [Indexed: 12/30/2022]
Abstract
Forensic DNA provides a striking contribution to the provision of justice worldwide. It has proven to be crucial in the investigative phase of an unsolved crime where a suspect needs to be identified, e.g. from a DNA database search both nationally and internationally. It is also a powerful tool in the assignment of evidential weight to the comparison of a profile of a person of interest and a crime scene profile. The focus of this document is the evaluation of autosomal profiles for criminal trials in the UK. A separate review covers investigation and evaluation of Y-STR profiles, investigation using autosomal profiles, kinship analysis, body identification and Forensic Genetic Genealogy investigations. In less than 40 years, forensic DNA profiling has developed from a specialist technique to everyday use. Borrowing on advances in genome typing technology, forensic DNA profiling has experienced a substantial increase in its sensitivity and informativeness. Alongside this development, novel interpretation methodologies have also been introduced. This document describes the state of the art and future advances in the interpretation of forensic DNA data.
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5
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Riman S, Iyer H, Vallone PM. Examining performance and likelihood ratios for two likelihood ratio systems using the PROVEDIt dataset. PLoS One 2021; 16:e0256714. [PMID: 34534241 PMCID: PMC8448353 DOI: 10.1371/journal.pone.0256714] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 08/07/2021] [Indexed: 11/30/2022] Open
Abstract
A likelihood ratio (LR) system is defined as the entire pipeline of the measurement and interpretation processes where probabilistic genotyping software (PGS) is a piece of the whole LR system. To gain understanding on how two LR systems perform, a total of 154 two-person, 147 three-person, and 127 four-person mixture profiles of varying DNA quality, DNA quantity, and mixture ratios were obtained from the filtered (.CSV) files of the GlobalFiler 29 cycles 15s PROVEDIt dataset and deconvolved in two independently developed fully continuous programs, STRmix v2.6 and EuroForMix v2.1.0. Various parameters were set in each software and LR computations obtained from the two software were based on same/fixed EPG features, same pair of propositions, number of contributors, theta, and population allele frequencies. The ability of each LR system to discriminate between contributor (H1-true) and non-contributor (H2-true) scenarios was evaluated qualitatively and quantitatively. Differences in the numeric LR values and their corresponding verbal classifications between the two LR systems were compared. The magnitude of the differences in the assigned LRs and the potential explanations for the observed differences greater than or equal to 3 on the log10 scale were described. Cases of LR < 1 for H1-true tests and LR > 1 for H2-true tests were also discussed. Our intent is to demonstrate the value of using a publicly available ground truth known mixture dataset to assess discrimination performance of any LR system and show the steps used to understand similarities and differences between different LR systems. We share our observations with the forensic community and describe how examining more than one PGS with similar discrimination power can be beneficial, help analysts compare interpretation especially with low-template profiles or minor contributor cases, and be a potential additional diagnostic check even if software in use does contain certain diagnostic statistics as part of the output.
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Affiliation(s)
- Sarah Riman
- Applied Genetics Group, National Institute of Standards and Technology, Gaithersburg, Maryland, United States of America
| | - Hari Iyer
- Statistical Design, Analysis, Modeling Group, National Institute of Standards and Technology, Gaithersburg, Maryland, United States of America
| | - Peter M. Vallone
- Applied Genetics Group, National Institute of Standards and Technology, Gaithersburg, Maryland, United States of America
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6
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Manabe S, Fujii K, Fukagawa T, Mizuno N, Sekiguchi K, Inoue K, Hashiyada M, Akane A, Tamaki K. Evaluation of probability distribution models for stutter ratios in the typing system of GlobalFiler and 3500xL Genetic Analyzer. Leg Med (Tokyo) 2021; 52:101906. [PMID: 34015722 DOI: 10.1016/j.legalmed.2021.101906] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 04/06/2021] [Accepted: 05/07/2021] [Indexed: 11/19/2022]
Abstract
As DNA typing systems have become increasingly sensitive in recent years, probability distribution models for back, forward, double-back, and minus 2-nt stutter ratios have been desired to be considered in DNA evidence interpretation using specific software programs. However, experimental investigations have been insufficient, especially for forward, double-back, and minus 2-nt stutters. In this study, we experimentally reevaluated the probability distribution models for each stutter ratio in the typing systems of GlobalFiler™ PCR Amplification Kit and 3500xL Genetic Analyzer from Thermo Fisher Scientific. In addition, to enhance the reliability of longest uninterrupted stretch (LUS) values and corrected allele numbers used in previously developed models for stutter ratios using sequence information (i.e., LUS model and multi-seq model), we propose the weighted average of LUS values and corrected allele numbers based on the number of observations in sequence-based population data. Back stutter ratios demonstrated a positive correlation with allele numbers (allele model) in eight loci, LUS values (LUS model) in eight loci, and corrected allele numbers (multi-seq model) in five loci. The forward stutter ratios (FSRs) of D22S1045 followed the LUS model. FSRs other than D22S1045 and double-back stutter ratios followed the LUS model by considering multiple loci together. Minus 2-nt stutter ratios observed in SE33 and D1S1656 did not increase with the increase in the allele numbers. The adopted models for each stutter ratio can be implemented in software programs for DNA evidence interpretation and enable a reliable interpretation of crime stain profiles in forensic caseworks.
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Affiliation(s)
- Sho Manabe
- Department of Legal Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan.
| | - Koji Fujii
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Takashi Fukagawa
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Natsuko Mizuno
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Kazumasa Sekiguchi
- Fourth Biological Section, National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan
| | - Kana Inoue
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
| | - Masaki Hashiyada
- Department of Legal Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Atsushi Akane
- Department of Legal Medicine, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Keiji Tamaki
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan
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Slooten K. The analogy between DNA kinship and DNA mixture evaluation, with applications for the interpretation of likelihood ratios produced by possibly imperfect models. Forensic Sci Int Genet 2020; 52:102449. [PMID: 33517022 DOI: 10.1016/j.fsigen.2020.102449] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 11/19/2020] [Accepted: 12/01/2020] [Indexed: 12/22/2022]
Abstract
Two main applications of forensic DNA analysis are the investigation of possible relatedness and the investigation whether a person left DNA in a trace. Both of these are usually carried out by the calculation of likelihood ratios. In the kinship case, it is standard to let the likelihood ratio express the support in favour of the investigated relatedness versus no relatedness, and in the investigation of traces, one by default compares the hypothesis that the person of interest contributed DNA, versus that he is unrelated to any of the actual contributors. In both cases however, we can also view the probabilistic procedure as an inference of the profile of the person we look for: in other words, in both cases we carry out probabilistic genotyping. In this article we use this general analogy to develop various more specific analogies between kinship and mixture likelihood ratios. These analogies help to understand the concepts that play a role, and also to understand the importance of the statistical modeling needed for DNA mixtures. In this article, we apply our findings to consider what we can and cannot conclude from a likelihood ratio in favour of contribution to a mixed DNA profile, if that is computed by a model whose specifics are not entirely known to us, or where we do not know whether they provide a good description of the stochastic effects involved in the generation of DNA trace profiles. We show that, if unrelated individuals are adequately modeled, we can give bounds on how often LR's coming from certain types of black box models may arise, both for persons who are actual contributors and who are unrelated. In particular we show that no model, provided it satisfies basic requirements, can overestimate the evidence found for actual contributors both often and strongly.
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Affiliation(s)
- Klaas Slooten
- Netherlands Forensic Institute, P.O. Box 24044, 2490 AA The Hague, The Netherlands; VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
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8
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An examination of STR nomenclatures, filters and models for MPS mixture interpretation. Forensic Sci Int Genet 2020; 48:102319. [DOI: 10.1016/j.fsigen.2020.102319] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 05/19/2020] [Accepted: 06/01/2020] [Indexed: 11/20/2022]
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9
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A top-down approach to DNA mixtures. Forensic Sci Int Genet 2020; 46:102250. [DOI: 10.1016/j.fsigen.2020.102250] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 12/23/2019] [Accepted: 01/16/2020] [Indexed: 01/16/2023]
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10
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Rodriguez JJRB, Bright JA, Salvador JM, Laude RP, De Ungria MCA. Probabilistic approaches to interpreting two-person DNA mixtures from post-coital specimens. Forensic Sci Int 2019; 300:157-163. [PMID: 31112838 DOI: 10.1016/j.forsciint.2019.04.037] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2019] [Revised: 03/26/2019] [Accepted: 04/29/2019] [Indexed: 01/23/2023]
Abstract
Biological samples submitted for sexual assault investigation typically involve mixtures of DNA from the victim and the assailant/s. Providing a statistical weight to such evidence may be mathematically complex and may be affected by subjective judgment of a human analyst. Software tools have been developed to address these issues. To contribute towards improving the system for routine DNA testing of sexual assault cases, we evaluated two likelihood ratio (LR) approaches: a semi-continuous model using LRmix Studio and a fully continuous approach employed in STRmix™ for interpreting two-person DNA mixtures. LRs conditioned on the presence of the receptive partner's DNA were calculated for a total of 102 two-person DNA samples from simulated mixtures and various post-coital samples. Our results highlight the importance of maximising information provided into the LR calculation to generate strong support for the true hypothesis. This can be achieved by recovering sufficient DNA from a sample to minimise risk of drop-out and increase peak intensities and by implementing a statistical model that utilises as much of the electropherogram information as possible. LRmix is open-source and can handle profiles with allelic drop-out and drop-ins, however stuttering is not modelled and requires manual removal by a DNA analyst especially for mixtures with low template components. STRmix™ makes effective use of all available information by incorporating into its biological model complicating aspects of a DNA profile such as degradation, allele drop-out and drop-in, stutters, and peak height variability.
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Affiliation(s)
- Jae Joseph Russell B Rodriguez
- DNA Analysis Laboratory, Natural Sciences Research Institute, College of Science, University of the Philippines Diliman, Quezon City, 1101 Philippines; Genetics and Molecular Biology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, Laguna, 4031 Philippines.
| | - Jo-Anne Bright
- Institute of Environmental Science and Research Ltd., Mt. Albert Science Centre, Auckland, New Zealand.
| | - Jazelyn M Salvador
- DNA Analysis Laboratory, Natural Sciences Research Institute, College of Science, University of the Philippines Diliman, Quezon City, 1101 Philippines.
| | - Rita P Laude
- Genetics and Molecular Biology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, Laguna, 4031 Philippines.
| | - Maria Corazon A De Ungria
- DNA Analysis Laboratory, Natural Sciences Research Institute, College of Science, University of the Philippines Diliman, Quezon City, 1101 Philippines.
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11
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Graversen T, Mortera J, Lago G. The Yara Gambirasio case: Combining evidence in a complex DNA mixture case. Forensic Sci Int Genet 2019; 40:52-63. [DOI: 10.1016/j.fsigen.2018.12.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2018] [Revised: 12/11/2018] [Accepted: 12/21/2018] [Indexed: 01/17/2023]
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12
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You Y, Balding D. A comparison of software for the evaluation of complex DNA profiles. Forensic Sci Int Genet 2019; 40:114-119. [DOI: 10.1016/j.fsigen.2019.02.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 01/22/2019] [Accepted: 02/13/2019] [Indexed: 10/27/2022]
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13
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McCord BR, Gauthier Q, Cho S, Roig MN, Gibson-Daw GC, Young B, Taglia F, Zapico SC, Mariot RF, Lee SB, Duncan G. Forensic DNA Analysis. Anal Chem 2019; 91:673-688. [PMID: 30485738 DOI: 10.1021/acs.analchem.8b05318] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Bruce R McCord
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Quentin Gauthier
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Sohee Cho
- Department of Forensic Medicine , Seoul National University , Seoul , 08826 , South Korea
| | - Meghan N Roig
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Georgiana C Gibson-Daw
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Brian Young
- Niche Vision, Inc. , Akron , Ohio 44311 , United States
| | - Fabiana Taglia
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Sara C Zapico
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Roberta Fogliatto Mariot
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
| | - Steven B Lee
- Forensic Science Program, Justice Studies Department , San Jose State University , San Jose , California 95192 , United States
| | - George Duncan
- Department of Chemistry , Florida International University , Miami , Florida 33199 , United States
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Vilsen SB, Tvedebrink T, Eriksen PS, Hussing C, Børsting C, Morling N. Modelling allelic drop-outs in STR sequencing data generated by MPS. Forensic Sci Int Genet 2018; 37:6-12. [DOI: 10.1016/j.fsigen.2018.07.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2018] [Revised: 07/14/2018] [Accepted: 07/23/2018] [Indexed: 10/28/2022]
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15
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The information gain from peak height data in DNA mixtures. Forensic Sci Int Genet 2018; 36:119-123. [DOI: 10.1016/j.fsigen.2018.06.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 05/23/2018] [Accepted: 06/07/2018] [Indexed: 11/21/2022]
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16
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Cowell RG. Computation of marginal distributions of peak-heights in electropherograms for analysing single source and mixture STR DNA samples. Forensic Sci Int Genet 2018; 35:164-168. [DOI: 10.1016/j.fsigen.2018.04.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 03/28/2018] [Accepted: 04/21/2018] [Indexed: 10/17/2022]
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17
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Manabe S, Morimoto C, Hamano Y, Fujimoto S, Tamaki K. Development and validation of open-source software for DNA mixture interpretation based on a quantitative continuous model. PLoS One 2017; 12:e0188183. [PMID: 29149210 PMCID: PMC5693437 DOI: 10.1371/journal.pone.0188183] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 11/02/2017] [Indexed: 02/01/2023] Open
Abstract
In criminal investigations, forensic scientists need to evaluate DNA mixtures. The estimation of the number of contributors and evaluation of the contribution of a person of interest (POI) from these samples are challenging. In this study, we developed a new open-source software “Kongoh” for interpreting DNA mixture based on a quantitative continuous model. The model uses quantitative information of peak heights in the DNA profile and considers the effect of artifacts and allelic drop-out. By using this software, the likelihoods of 1–4 persons’ contributions are calculated, and the most optimal number of contributors is automatically determined; this differs from other open-source software. Therefore, we can eliminate the need to manually determine the number of contributors before the analysis. Kongoh also considers allele- or locus-specific effects of biological parameters based on the experimental data. We then validated Kongoh by calculating the likelihood ratio (LR) of a POI’s contribution in true contributors and non-contributors by using 2–4 person mixtures analyzed through a 15 short tandem repeat typing system. Most LR values obtained from Kongoh during true-contributor testing strongly supported the POI’s contribution even for small amounts or degraded DNA samples. Kongoh correctly rejected a false hypothesis in the non-contributor testing, generated reproducible LR values, and demonstrated higher accuracy of the estimated number of contributors than another software based on the quantitative continuous model. Therefore, Kongoh is useful in accurately interpreting DNA evidence like mixtures and small amounts or degraded DNA samples.
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Affiliation(s)
- Sho Manabe
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Chie Morimoto
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Yuya Hamano
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
- Forensic Science Laboratory, Kyoto Prefectural Police Headquarters, Kyoto, Japan
| | - Shuntaro Fujimoto
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Keiji Tamaki
- Department of Forensic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
- * E-mail:
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Peters KC, Swaminathan H, Sheehan J, Duffy KR, Lun DS, Grgicak CM. Production of high-fidelity electropherograms results in improved and consistent DNA interpretation: Standardizing the forensic validation process. Forensic Sci Int Genet 2017; 31:160-170. [DOI: 10.1016/j.fsigen.2017.09.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 08/31/2017] [Accepted: 09/06/2017] [Indexed: 01/08/2023]
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19
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Slooten K. Accurate assessment of the weight of evidence for DNA mixtures by integrating the likelihood ratio. Forensic Sci Int Genet 2016; 27:1-16. [PMID: 27914277 DOI: 10.1016/j.fsigen.2016.11.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Revised: 10/26/2016] [Accepted: 11/06/2016] [Indexed: 01/24/2023]
Abstract
Several methods exist for weight of evidence calculations on DNA mixtures. Especially if dropout is a possibility, it may be difficult to estimate mixture specific parameters needed for the evaluation. For semi-continuous models, the LR for a person to have contributed to a mixture depends on the specified number of contributors and the probability of dropout for each. We show here that, for the semi-continuous model that we consider, the weight of evidence can be accurately obtained by applying the standard statistical technique of integrating the likelihood ratio against the parameter likelihoods obtained from the mixture data. This method takes into account all likelihood ratios belonging to every choice of parameters, but LR's belonging to parameters that provide a better explanation to the mixture data put in more weight into the final result. We therefore avoid having to estimate the number of contributors or their probabilities of dropout, and let the whole evaluation depend on the mixture data and the allele frequencies, which is a practical advantage as well as a gain in objectivity. Using simulated mixtures, we compare the LR obtained in this way with the best informed LR, i.e., the LR using the parameters that were used to generate the data, and show that results obtained by integration of the LR approximate closely these ideal values. We investigate both contributors and non-contributors for mixtures with various numbers of contributors. For contributors we always obtain a result close to the best informed LR whereas non-contributors are excluded more strongly if a smaller dropout probability is imposed for them. The results therefore naturally lead us to reconsider what we mean by a contributor, or by the number of contributors.
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Affiliation(s)
- Klaas Slooten
- Netherlands Forensic Institute, P.O. Box 24044, 2490 AA The Hague, The Netherlands; VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
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