Comparison and interpretation of impressed marks left by a firearm on cartridge cases – Towards an operational implementation of a likelihood ratio based technique

Forensic comparison of fired cartridge cases: Feature-extraction methods for feature-based calculation of likelihood ratios

“…To our knowledge, there is no published research describing calculation of likelihood ratios using statistical models applied to features separately extracted from each cartridge case, but there are a number of papers that describe calculation of likelihood ratios based on similarity scores. The most commonly used similarity score has been a correlation coefficient between pairs of digital images, calculated over the whole of or selected portions of the firing-pin impression or of the breech-face region (Riva & Champod [ 47 ]; Dong et al [ 48 ]; Mattijssen et al [ 7 ]; Riva et al [ 49 ]). Other similarity scores used have been based on Euclidian distance between pairs of digital images, and on instantaneous angles on the surfaces of pairs of 3D images (Riva & Champod [ 47 ]; Riva et al [ 49 ]).…”

“…The most commonly used similarity score has been a correlation coefficient between pairs of digital images, calculated over the whole of or selected portions of the firing-pin impression or of the breech-face region (Riva & Champod [ 47 ]; Dong et al [ 48 ]; Mattijssen et al [ 7 ]; Riva et al [ 49 ]). Other similarity scores used have been based on Euclidian distance between pairs of digital images, and on instantaneous angles on the surfaces of pairs of 3D images (Riva & Champod [ 47 ]; Riva et al [ 49 ]). The most commonly used models have fitted kernel density distributions (Riva & Champod [ 47 ]; Dong et al [ 48 ]; Mattijssen et al [ 7 ]; Riva et al [ 49 ]).…”

Evaluation of distance‐based approaches for forensic comparison: Application to hand odor evidence

“…The most common approach of forensic science to this problem is to estimate a likelihood ratio (LR), i.e., the ratio of the joint probability of occurrence of the two traces under the hypothesis that they arose from the same source and under the hypothesis that they arose from different sources. A convenient solution is to replace the joint probability of the traces by the probability of a distance between the two traces quantifying their dissimilarity (6, 9–14,). If, as is most often the case, the distance is scalar, there is an important loss of information.…”

Firearm examination: Examiner judgments and computer‐based comparisons

“…Currently, the application of such methods is limited to automated database searches, but these methods could also be used to evaluate the evidence. Several such methods have been developed, typically relying on 3D surface topography measurements of striation and impression patterns (e.g., [24,25,[26][27][28][29][30]). Computer algorithms compare these topography measurements and provide a comparison score based on the degree of similarity.…”

“…Computer algorithms compare these topography measurements and provide a comparison score based on the degree of similarity. These comparison scores are then used to make a source decision and to assess the error rate of that decision [27,31], or to determine the evidential strength of a comparison [24,25,30]. The likelihood ratio (LR) is used to express the evidential strength.…”