Nicole Egli

Computation of likelihood ratios in fingerprint identification for configurations of any number of minutiae.

ABSTRACT: Recent court challenges have highlighted the need for statistical research on fingerprint identification. This paper proposes a model for computing likelihood ratios (LRs) to assess the evidential value of comparisons with any number of minutiæ. The model considers minutiae type, direction and relative spatial relationships. It expands on previous work on three minutiae by adopting a spatial modeling using radial triangulation and a probabilistic distortion model for assessing the numerator of the LR. The model has been tested on a sample of 686 ulnar loops and 204 arches. Features vectors used for statistical analysis have been obtained following a preprocessing step based on Gabor filtering and image processing to extract minutiae data. The metric used to assess similarity between two feature vectors is based on an Euclidean distance measure. Tippett plots and rates of misleading evidence have been used as performance indicators of the model. The model has shown encouraging behavior with low rates of misleading evidence and a LR power of the model increasing significantly with the number of minutiæ. The LRs that it provides are highly indicative of identity of source on a significant proportion of cases, even when considering configurations with few minutiæ. In contrast with previous research, the model, in addition to minutia type and direction, incorporates spatial relationships of minutiæ without introducing probabilistic independence assumptions. The model also accounts for finger distortion.

Computation of Likelihood Ratios in Fingerprint Identification for Configurations of Three Minutiae

ABSTRACT: Recent challenges to fingerprint evidence have brought forward the need for peer‐reviewed scientific publications to support the evidential value assessment of fingerprint. This paper proposes some research directions to gather statistical knowledge of the within‐source and between‐sources variability of configurations of three minutiæ on fingermarks and fingerprints. This paper proposes the use of the likelihood ratio (LR) approach to assess the value of fingerprint evidence. The model explores the statistical contribution of configurations of three minutiae using Tippett plots and related measures to assess the quality of the system. Features vectors used for statistical analysis have been obtained following a preprocessing step based on Gabor filtering and image processing to extract minutia position, type, and direction. Spatial relationships have been coded using Delaunay triangulation. The metric, used to assess similarity between two feature vectors is based on an Euclidean distance measure. The within‐source variability has been estimated using a sample of 216 fingerprints from four fingers (two donors). Between‐sources variability takes advantage of a database of 818 ulnar loops from randomly selected males. The results show that the data‐driven approach adopted here is robust. The magnitude of LRs obtained under the prosecution and defense propositions stresses upon the major evidential contribution that small portions of fingermark, containing three minutiæ, can provide regardless of its position on the general pattern.

Integrated vs. differentiated school systems and their impact on delinquency

The Swiss school system is based on selectivity and classification. From a relatively young age, students are assigned to levels leading to different professional orientations, from apprenticeship to university. Using data from the Swiss ISRD-2 (Second International Self-Reported Delinquency Study), this study analyses the link between Swiss schools and delinquency, as measured by prevalence in the 12 months before filling out the questionnaire. Three dependent variables with large prevalence rates were considered: shoplifting, vandalism and a composite variable, all offences. The results were generated using two analytical methods, controlling for sociodemographic and individual characteristics and variables related to the family and the neighbourhood. The analyses reveal that being in the lowest track either in the school itself or in the school system is not related to increased risk of delinquency.