The authors report on two interlaboratory studies designed to do two things: first, to assess the proposed method for examining, documenting, and interpreting physical fits of duct tapes using standardized qualitative descriptors and quantitative metrics, and second, to refine the proposed method and training provided to participants, with an overall goal of incorporating this feedback to develop consensus protocols that can be practical and usable by the scientific community.
This paper describes two interlaboratory studies of a novel method for duct tape physical fit examinations, through the collaboration of 38 forensic practitioners from 23 laboratories. Each participant analyzes seven duct tape pairs, representing casework-like fits and non-fits. The ground truth is maintained blind to participants, who are instructed to follow a pilot method to examine the tapes, document bin-by-bin observations, estimate the edge similarity score (ESS) as a metric for the quality of the fit, and report a conclusion. The results from 266 examinations are compared across participants and to a consensus ESS established prior to administering the studies by an independent panel. The participants’ feedback from the first study is applied to refine the instructions, training, and reporting tools for the second exercise. Both interlaboratory studies evaluate the inter-examiner variability using performance rates based on ESS results and conclusions provided by the participants, showing an overall accuracy of 95 percent and 99 percent for the first and second exercises, respectively. When the data is compared to the consensus ESS from the independent panel, the error rate improves from 9.3 to 5.5 percent in the second study. When assessing the ESS data using z-scores, most participants' results were satisfactory, with eight cautionary and two insufficient results in the first study, and seven cautionary and no insufficient results in the second trial. Overall, the inter-laboratory performances indicate that the proposed qualitative and quantitative criteria assist practitioners in arriving at reproducible assessments of the quality of the fit and demonstrable conclusions. (Publisher Abstract Provided)