Modeling forward stutter: Toward increased objectivity in forensic <scp>DNA</scp> interpretation

Bright, Jo‐Anne; Buckleton, John; Taylor, Duncan; Fernando, M.A.C.S.S.; Curran, James M.

doi:10.1002/elps.201400044

Cited by 24 publications

(12 citation statements)

References 17 publications

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“…Stutter is a PCR amplification artifact caused by ‘strand slippage’ that generates non-allelic peaks in the signal that can be hard to distinguish from allelic peaks from minor contributors to a DNA mixture [ 18 ]. The models utilized by Puch-Solis et al [ 5 ], Cowell et al [ 4 ] and Perlin et al [ 2 ] to encapsulate stutter differ from each other and account for reverse stutter (stutter that is one repeat unit shorter than the allele), while the model in [ 19 ] also incorporates the possibility of forward stutter (stutter that is one repeat unit larger than the allele).…”

Section: Introductionmentioning

confidence: 99%

Four model variants within a continuous forensic DNA mixture interpretation framework: Effects on evidential inference and reporting

et al. 2018

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Continuous mixture interpretation methods that employ probabilistic genotyping to compute the Likelihood Ratio (LR) utilize more information than threshold-based systems. The continuous interpretation schemes described in the literature, however, do not all use the same underlying probabilistic model and standards outlining which probabilistic models may or may not be implemented into casework do not exist; thus, it is the individual forensic laboratory or expert that decides which model and corresponding software program to implement. For countries, such as the United States, with an adversarial legal system, one can envision a scenario where two probabilistic models are used to present the weight of evidence, and two LRs are presented by two experts. Conversely, if no independent review of the evidence is requested, one expert using one model may present one LR as there is no standard or guideline requiring the uncertainty in the LR estimate be presented. The choice of model determines the underlying probability calculation, and changes to it can result in non-negligible differences in the reported LR or corresponding verbal categorization presented to the trier-of-fact. In this paper, we study the impact of model differences on the LR and on the corresponding verbal expression computed using four variants of a continuous mixture interpretation method. The four models were tested five times each on 101, 1-, 2- and 3-person experimental samples with known contributors. For each sample, LRs were computed using the known contributor as the person of interest. In all four models, intra-model variability increased with an increase in the number of contributors and with a decrease in the contributor’s template mass. Inter-model variability in the associated verbal expression of the LR was observed in 32 of the 195 LRs used for comparison. Moreover, in 11 of these profiles there was a change from LR > 1 to LR < 1. These results indicate that modifications to existing continuous models do have the potential to significantly impact the final statistic, justifying the continuation of broad-based, large-scale, independent studies to quantify the limits of reliability and variability of existing forensically relevant systems.

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Section: Introductionmentioning

confidence: 99%

Four model variants within a continuous forensic DNA mixture interpretation framework: Effects on evidential inference and reporting

et al. 2018

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“…It is hypothesised here that forward stutter peak height does depend on parent peak height, however in [18] only the highest few percent of all forward stutter peaks were seen and this caused dependencies to be hidden. Figure 2 shows that from all applicable forward stutter positions only a few percent had forward stutters observed (shown as the black, ‗Original work' line).…”

Section: Forward Stutter Ratiomentioning

confidence: 81%

“…Forward stutter ratio (FSR) is quantified by calculating the ratio of the observed height of the forward stutter peak (O a+1 ) to the observed height of the allelic peak (O a ). stutter height such as parent allele height (O a ), locus and the longest uninterrupted sequence (LUS) were found unsuitable for predicting the height of forward stutter peaks for all tetra and pentanucleotide repeats [18]. This result was surprising given the known mechanism of stutter generation and the anecdotal observations of forward stutter being observed commonly for parent peaks that had high peak heights (suggesting that there is indeed some dependence of forward stutter on parent peak height).…”

Section: Forward Stutter Ratiomentioning

confidence: 99%

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Validating multiplexes for use in conjunction with modern interpretation strategies

Taylor

Bright

McGoven

et al. 2016

Forensic Science International: Genetics

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In response to requests from the forensic community, commercial companies are generating larger, more sensitive, and more discriminating STR multiplexes. These multiplexes are now applied to a wider range of samples including complex multi-person mixtures. In parallel there is an overdue reappraisal of profile interpretation methodology. Aspects of this reappraisal include 1. The need for a quantitative understanding of allele and stutter peak heights and their variability, 2. An interest in reassessing the utility of smaller peaks below the often used analytical threshold, 3. A need to understand not just the occurrence of peak drop-in but also the height distribution of such peaks, and 4. A need to understand the limitations of the multiplex-interpretation strategy pair implemented. In this work we present a full scheme for validation of a new multiplex that is suitable for informing modern interpretation practice. We predominantly use GlobalFiler™ as an example multiplex but we suggest that the aspects investigated here are fundamental to introducing any multiplex in the modern interpretation environment.

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“… 1 The scope of these procedures is large and includes topics such as complex modeling of products (e.g., stutters) of the PCR amplification of STRs (e.g., Bright et al, 2014 ; Gittelson et al, 2014 ) and the study of the sensitivity of expressions of probative value due to the use of particular statistical techniques (e.g., MCMC techniques, see for example Bright et al, 2015 ). …”

mentioning

confidence: 99%

The Importance of Critically Examining the Level of Propositions When Evaluating Forensic DNA Results

Biedermann

Hicks

2016

Front. Genet.

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Modeling forward stutter: Toward increased objectivity in forensic DNA interpretation

Cited by 24 publications

References 17 publications

Four model variants within a continuous forensic DNA mixture interpretation framework: Effects on evidential inference and reporting

Four model variants within a continuous forensic DNA mixture interpretation framework: Effects on evidential inference and reporting

Validating multiplexes for use in conjunction with modern interpretation strategies

The Importance of Critically Examining the Level of Propositions When Evaluating Forensic DNA Results

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