Optimization of a Statistical Algorithm for Objective Comparison of Toolmarks

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2015-03-01
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Spotts, Ryan
Chumbley, L. Scott
Ekstrand, Laura
Zhang, Song
Kreiser, James
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Materials Science and Engineering
Materials engineers create new materials and improve existing materials. Everything is limited by the materials that are used to produce it. Materials engineers understand the relationship between the properties of a material and its internal structure — from the macro level down to the atomic level. The better the materials, the better the end result — it’s as simple as that.
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Ames National LaboratoryMaterials Science and Engineering
Abstract

Due to historical legal challenges, there is a driving force for the development of objective methods of forensic toolmark identification. This study utilizes an algorithm to separate matching and nonmatching shear cut toolmarks created using fifty sequentially manufactured pliers. Unlike previously analyzed striated screwdriver marks, shear cut marks contain discontinuous groups of striations, posing a more difficult test of algorithm applicability. The algorithm compares correlation between optical 3D toolmark topography data, producing a Wilcoxon rank sum test statistic. Relative magnitude of this metric separates the matching and nonmatching toolmarks. Results show a high degree of statistical separation between matching and nonmatching distributions. Further separation is achieved with optimized input parameters and implementation of a “leash” preventing a previous source of outliers—however complete statistical separation was not achieved. This paper represents further development of objective methods of toolmark identification and further validation of the assumption that toolmarks are identifiably unique.

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This is the peer-reviewed version of the following article: Spotts, Ryan, L. Scott Chumbley, Laura Ekstrand, Song Zhang, and James Kreiser. "Optimization of a statistical algorithm for objective comparison of toolmarks." Journal of Forensic Sciences 60, no. 2 (2015): 303-314, which has been published in final form at DOI: 10.1111/1556-4029.12642 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Posted with permission.

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Wed Jan 01 00:00:00 UTC 2014
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