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Establishing Exclusion Criteria and the Significance of Inclusion for Complex Low-Template DNA Mixtures

NCJ Number
Date Published
October 2018
Catherine Grgicak
Publication Type
Research (Applied/Empirical), Report (Study/Research), Report (Grant Sponsored), Program/Project Description
Grant Number(s)
This research addressed the need to increase the understanding of complex forensic DNA interpretation and to develop a novel approach for interpreting low-template DNA samples that contain many contributors.
Specifically, the project had the following three objectives: 1) increase the fundamental understanding of the relationship between DNA input and signal so as to provide recommendations for DNA validation experimental design; 2) provide algorithms and prototype software that combines the features of a fully continuous model to calculate the LR and its distribution, conditioned on the defense hypothesis; and 5) provide interpretation approaches that use novel algorithms and signal information produced by the laboratory to reduce the need to continuously re-evaluate validation data. The method was tested on 306 1-, 2-, and 3-person electropherograms containing between 0.016 and 1 ng of DNA. The amount of template DNA from the contributor had an impact on the LR; small LRs arose from contributors with low template masses, indicating that high levels of dropout and stutter could decrease the probability of the evidence under the prosecution's hypothesis, even for true contributors. Since researchers used 109 samples to calculate the p-value; the lowest possible p-value that can be achieved is 10-9 , and this was obtained in all the cases in which the LR was greater than 108. The results from MatchIt were found to be repeatable after duplicate runs on all the samples in the testing set. 3 figures, 2 tables, and 3 references
Date Created: December 17, 2018