Validation of a DNA mixture statistics tool incorporating allelic drop-out and drop-in

Mitchell, Adele A.; Tamariz, Jeannie; O’Connell, Kathleen; Ducasse, Nubia; Budimlija, Zoran; Prinz, Mechthild; Caragine, Theresa

doi:10.1016/j.fsigen.2012.08.007

Cited by 57 publications

(27 citation statements)

References 32 publications

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“…With regard to the parameter values examined in this study (i.e., the symmetric vs. the conservative preference structure, and a probability of allele drop-in of 0.01 vs. 0.05 per locus), it is the utility function’s preference structure that had the greater impact. It is possible that a larger probability of allele drop-in might have a larger impact than the results observed in this study, yet according to the values reported in the literature [e.g., 1, 3, 19, 20], it is not reasonable to assume a probability of allele drop-in greater than 0.05 per locus.…”

Section: Discussionmentioning

confidence: 49%

Low-template DNA: A single DNA analysis or two replicates?

Gittelson

Steffen

Coble

2016

Forensic Science International

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This study investigates the following two questions: (1) Should the DNA analyst concentrate the DNA extract into a single amplification or should he/she split it up to do two replicates? (2) Given the electropherogram obtained from a first analysis, is it worthwhile for the DNA analyst to invest in obtaining a second replicate? A decision-theoretic approach addresses these questions by quantitatively expressing the expected net gain (ENG) of each DNA analysis of interest. The results indicate that two replicates generally have a greater ENG than a single DNA analysis for DNA quantities capable of producing two replicates having an average allelic peak height as low as 43 rfu. This supports the position that two replicates increase the information content with regard to a single analysis.

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Section: Discussionmentioning

confidence: 49%

Low-template DNA: A single DNA analysis or two replicates?

Gittelson

Steffen

Coble

2016

Forensic Science International

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“…It goes beyond these methods by eliminating nuisance parameters automatically via maximization of penalized likelihoods, avoiding the use of external calibration data specific to the profiling protocol used, as required by other methods (9). Even with extensive calibration data, estimation of dropout and dropin rates for the specific conditions of a crime sample cannot be precise, but precise estimates are not required: "Best fit" (in the sense of maximum penalized likelihood) values under each of the competing hypotheses provide a fair evaluation of the WoE.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, remote shared ancestry ("coancestry") of X with Q is modeled using the population genetics parameter F ST (17). Typically, in US forensic practice, F ST (also called θ) is only used to model intraindividual genetic correlations (i.e., excess homozygosity) (9). However, intraindividual correlations are of little relevance to evidential weight.…”

Section: Methodsmentioning

confidence: 99%

“…In previous formulations (5)(6)(7)(8)(9)(10), the likelihood at a locus in a profiling run is the product over all allelic positions in the epg of one of four possible terms, according to whether or not the corresponding allele is represented in the crime scene profile (CSP) and whether or not it is included in the profiles of any of the hypothesized contributors (Materials and Methods). I introduce here a fifth possibility corresponding to an absence of information about whether the allele is present, irrespective of whether or not it is included in the profile of a hypothesized contributor.…”

Section: Case Of Knox and Sollecitomentioning

confidence: 99%

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Evaluation of mixed-source, low-template DNA profiles in forensic science

Balding

2013

Proc. Natl. Acad. Sci. U.S.A.

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Enhancements in sensitivity now allow DNA profiles to be obtained from only tens of picograms of DNA, corresponding to a few cells, even for samples subject to degradation from environmental exposure. However, low-template DNA (LTDNA) profiles are subject to stochastic effects, such as "dropout" and "dropin" of alleles, and highly variable stutter peak heights. Although the sensitivity of the newly developed methods is highly appealing to crime investigators, courts are concerned about the reliability of the underlying science. High-profile cases relying on LTDNA evidence have collapsed amid controversy, including the case of Hoey in the United Kingdom and the case of Knox and Sollecito in Italy. I argue that rather than the reliability of the science, courts and commentators should focus on the validity of the statistical methods of evaluation of the evidence. Even noisy DNA evidence can be more powerful than many traditional types of evidence, and it can be helpful to a court as long as its strength is not overstated. There have been serious shortcomings in statistical methods for the evaluation of LTDNA profile evidence, however. Here, I propose a method that allows for multiple replicates with different rates of dropout, sporadic dropins, different amounts of DNA from different contributors, relatedness of suspected and alternate contributors, "uncertain" allele designations, and degradation. R code implementing the method is open source, facilitating wide scrutiny. I illustrate its good performance using real cases and simulated crime scene profiles. Reliability of Low-Template DNA Profiling P roblems with the courtroom use of low-template DNA (LTDNA) profiles were brought into sharp focus in the United Kingdom in 2007, with the collapse of a trial arising from the Omagh bombing in Northern Ireland in 1998. This crime killed 29 people and injured many more; consequently, early termination of the trial and acquittal of the defendant attracted widespread adverse publicity. The judge gave several reasons, but it was his critical appraisal of the LTDNA evidence that captured headlines. In response to the controversy, a report reviewing LTDNA evidence (1) was commissioned by the UK Forensic Science Regulator. The report found the underlying science to be "sound" and LTDNA profiling to be "fit for purpose," although admitting that there was lack of agreement "on how LTDNA profiles are to be interpreted."I suggest that these comments are somewhat contradictory: Without valid methods of assessing evidential strength, a technique cannot be fit for purpose in the criminal justice system. Fig. 1 shows part of the electropherogram (epg) giving the results from replicate LTDNA profiling runs in a crime investigation. The two epgs show substantial similarity yet also important differences: For example, the 17 allele at locus D19 is detected in Fig. 1 (Left) but not in Fig. 1 (Right), yet the reverse is true for the 11 allele. Is a technology that produces such variable results reliable? This is often asked by legal comme...

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“…However, the small number of STRs in those kits (up to 23) may result in low statistical significance of an inclusion in complex mixtures with more than three contributors or for cases where the contribution of the suspect is relatively low. In a recent publication, Mitchell et al [7] presented a method for the analysis of complex DNA mixtures using standard STRs and allowing for allelic drop-out and drop-in. However, applying this method on mixtures composed of more than two contributors typed with a standard STR kit resulted in relatively low likelihood ratio (LR) values for non-major contributors.…”

Section: Introductionmentioning

confidence: 99%