Forensic Footwear Reliability: Part II-Range of Conclusions, Accuracy, and Consensus

Between February 2017 and August 2018, West Virginia University conducted a reliability study to determine expert performance among forensic footwear examiners in the United States. Throughout the study's duration, 70 examiners each performed 12 comparisons and reported a total of 840 conclusions. In order to assess the accuracy of conclusions, the similarities and differences between mated and nonmated pairs were evaluated according to three criteria: (i) inherent agreement/disagreement in class, wear, and randomly acquired features, (ii) limitations as a function of questioned impression quality, clarity, and totality, and (iii) adherence to the Scientific Working Group for Shoeprint and Tire Tread Evidence (SWGTREAD) 2013 conclusion standard. Using these criteria, acceptable/expected categorical conclusions were defined. Preliminary results from this study are divided into a series of three summaries. This manuscript (Part II) reports accuracy and reproducibility. For mated pairs, accuracy equals 76.3% ± 13.0% (median of 78.6% and a 90% confidence interval between 72.2% and 80.0%). For nonmated pairs, accuracy equals 87.4% ± 9.24% (median of 91.4% and a 90% confidence interval between 84.7% and 89.8%). In addition, the community assessed agreement (denoted by IQR) of reported results equals the research team's accepted/expected conclusions for 10 out of 12 comparisons. In terms of reproducibility, the 90% confidence interval for consensus was computed and found to equal 0.71-0.86 (median of 0.77) for the combined dataset. Although based on a limited sample size, these results provide a baseline estimate of accuracy and consensus/reproducibility as a function of the existing seven-point SWGTREAD 2013 conclusion standard.