Computation of Likelihood Ratios in Fingerprint Identification for Configurations of Any Number of Minutiæ
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.
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ABSTRACT: In recent times, some studies have explored the forensic application of dermatoglyphic traits such as the epidermal ridge breadth or ridge density (RD) toward the inference of sex and population from fingerprints of unknown origin, as it has been demonstrated that there exist significant differences of fingerprints between sexes and between populations. Part of the population differences found between these studies could be of methodological nature, due both to the lack of standardisation in the position of the counting area, as well as to the differences in the method used for obtaining the fingerprint. Therefore, the aim of this study was to check whether there are differences between the RD of fingerprints depending on where the counting area is placed and how the fingerprints are obtained. Fingerprints of each finger were obtained from 102 adult Spanish subjects (50 females and 52 males), using two methods (plain and rolled). The ridge density of each fingerprint was assessed in five different areas of the dactylogram: two closer to the core area (one on the radial and the other on the ulnar side), two closer to the outermost area of each of the sides (radial and ulnar), and another one in the proximal region of the fingertip. Regardless of the method used and of the position of the counting area, thumbs and forefingers show a higher RD than middle, ring, and little fingers in both sexes, and females present a higher RD than males in all areas and fingers. In both males and females, RD values on the core region are higher than those on the outer region, irrespective of the technique of fingerprinting used (rolled or plain). Regardless of the sex and location of the count area (core or outer), the rolled fingerprints exhibit RD greater than that of the plain ones in both radial and proximal areas, whereas the trend is inverted in the ulnar area, where rolled fingerprints demonstrate RD lesser than that of the plain ones. Therefore, in order for the results of different studies to be comparable, it is necessary to standardise the position of the count area and to use the same method of obtaining the fingerprint, especially when involving a forensic application.Science & Justice 01/2013; 54(3). DOI:10.1016/j.scijus.2013.11.004 · 1.42 Impact Factor
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ABSTRACT: In recent years, both scientific and judicial sources have highlighted the need for more knowledge about minutiae variability, in order to improve their statistical application to fingerprint identification. In line with this trend toward improving our knowledge of this subject, the aim of the present study was to calculate the frequency with which 20 types of minutiae appeared in 2780 fingerprint impressions obtained from 278 individuals from two Argentinian population samples (100 individuals from Ramal and 178 from Puna-Quebrada). The different types of minutiae were located, identified, and quantified visually in two areas on the fingerprint, the inside and outside of a circle, the radius of which cut fifteen ridges perpendicularly, starting from the center cut of the axes defining the sectors. The non-equiprobability found in both population samples for the different minutiae types studied demonstrated that the evidential weight provided by these characteristics is not the same when applied in identification processes, whether used quantitatively (numerical standard) or qualitatively (holistic method). The results obtained for both populations were compared statistically with those published previously for a Spanish population sample, which had been collected using the same methodology. This comparison has enabled us to demonstrate, for the first time, the existence of significant differences between populations in minutiae frequencies, independently from the main pattern type.Forensic science international 07/2012; 222(1-3):266-76. DOI:10.1016/j.forsciint.2012.07.003 · 2.12 Impact Factor
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ABSTRACT: Read before The Royal Statistical Society on Wednesday, September 28th, 2011, the Presi-dent, Professor V. S. Isham, in the Chair ] Summary. The fingerprint has, with considerable justification, come to be regarded as the acme of forensic identification. Over the last century, millions of cases have been resolved worldwide because of marks left at crime scenes. The comparison methodology has not evolved greatly during its history and it is universal practice to present fingerprint evidence to a court as a categoric opinion of identification or exclusion, or to classify the evidence as inconclusive and not to report it. There has been a growing movement to supplement the fingerprint examination process by one that has a statistical model, supported by appropriate databases for calculating numerical measures of weight of evidence. The movement calls for the establishment of a logi-cal framework for informing conclusions, based on explicit assumptions and data and open to revision and improvement. The aim is to enable the numerical evaluation of evidence that would currently be reported as a categorical identification and also of evidence that would currently be classified as inconclusive. The paper presents the results of a project carried out by the Forensic Science Service that aims to attain this goal. After a historical review, we describe a formal model for assigning numerical values to configurations of minutiae in fingerprints. We describe how the parameters of the model have been optimized to take account of interoperator variability and distortion of the finger pad, and we present the results of a substantial validation experiment that was based on searches that have been carried out on the US national fingerprint database of approximately 600 million fingerprints.Journal of the Royal Statistical Society Series A (Statistics in Society) 04/2012; 175(2):1-26. DOI:10.2307/23251242 · 1.57 Impact Factor