Estimate of the Random Match Frequency of Acquired Characteristics in Footwear: Part I - Impressions in Blood

• NCJ Number: 308690
• Journal: Science and Justice Volume: 64 Issue: 1 Dated: January 2024 Pages: 117-133
• Author(s): Alyssa N. Smale; Jacqueline A. Speir
• Date Published: January 2024
• Length: 17 pages
• Grant Number(s): 2013-DN-BX-K043
• Agencies: NIJ-Sponsored
• Publication Type: Research (Applied/Empirical)
• Award: A Quantitative Assessment of Shoeprint Accidental Patterns with Implications Regarding Similarity, Frequency and Chance Association of Features

Annotation

This is Part I of a study estimating the random match frequency of acquired characteristics in footwear.

Abstract

The aim of this study was to estimate random match frequency of randomly acquired characteristics (RAC-RMF) for laboratory-simulated crime scene impressions. Part I of this investigation reports this metric using a dataset of more than 160 questioned impressions created in blood and deposited on tile. Results indicated that RACs in blood impressions were typically smaller, and therefore exhibited a two-thirds increase in the number of indistinguishable pairs compared to their mated test impressions. This research shows that RACs in questioned impressions of the type expected in casework co-occur in position and geometry with RACs in non-mated test impressions. Since theoretical models have traditionally been the basis for estimating RAC-RMF in footwear, the overall contribution of this research to the forensic footwear community is a calibration of this estimate based on empirical data. A total of 759 RACs were identified in the blood impressions and compared to RACs with positional similarity in test impressions from 1,299 unrelated outsoles. Geometric similarity was quantified using a combination of visual comparisons and mathematical modeling based on percent area overlap. For shoes contributing at least one RAC, relative RAC-RMF values ⩾ 0.0008 were encountered at a rate between 3.4% and 34% for the blood impressions examined in this study. Part II of this investigation provides analogous results based on dust impressions deposited on paper and tile. The results in Part I and Part II are specific to randomly acquired characteristics and do not translate into an impression-wide RMF estimate. (Published Abstract Provided)