Significance of Association in Tool Mark Characterization.

摘要

One weakness that currently exists in the field of comparative examination of evidence is the general failure of current approaches to adequately assess the significance of association through quantitative measures that provide a statistical evaluation of evidence. While various efforts have been made and methodologies employed over the years, such as the measurement of consecutive matching striations, tool mark comparisons remain difficult to quantify in a robust statistically valid sense. While the desire to develop a methodology that allows the examiner to assign confidence levels and predict error rates is universal, the unfortunate truth is that such a description (similar to what is possible in the field of DNA) is an unattainable goal in toolmark analysis since the population will continually increase and the variability cannot be satisfactorily defined. However, this is not to say that statistical relevance cannot be assigned to toolmark examination. Relevance can be assigned if one is careful about the structure of the study attempted. In a recent study of tool marks produced by sequentially made screwdriver tips the authors developed a computer algorithm that was able to reliably separate matching tool marks from those that do not match using an analysis based on Mann-Whitney U-statistics applied to data files containing 2-dimensional information obtained using an optical profilometer. These successful results indicate that significance of association can be accomplished by statistical evaluation of the data files. The work carried in the present project (and discussed in this report) built upon this success by providing additional statistical information that will increase the relevance of the measurements obtained. Thus, the overall goal of this work was to increase the statistical relevance of toolmark analysis. To achieve this goal two distinct objectives were identified.