Publication trends in forensic science research: Friction ridge discipline.

2019 commemorates the 10 year anniversary of the National Academy of Sciences report, "Strengthening Forensic Science in the United States: A Path Forward," and one valuable way to measure progress in forensic science is through published research. The purpose of this study is to examine where the friction ridge discipline stands with respect to published research. Two time periods were selected (2005-2009 and 2010-2014) and two different methods were used to describe research growth and publication trends in this discipline. A bibliometric review was conducted using an online literature-indexing tool, Web of Science™, as well as an empirical method involving subject matter experts. Both methods showed an increased number of friction ridge articles published in scientific journals over time.

Gaze behavior and cognitive states during fingerprint target group localization.

BACKGROUND: The comparison of fingerprints by expert latent print examiners generally involves repeating a process in which the examiner selects a small area of distinctive features in one print (a target group), and searches for it in the other print. In order to isolate this key element of fingerprint comparison, we use eye-tracking data to describe the behavior of latent fingerprint examiners on a narrowly defined "find the target" task. Participants were shown a fingerprint image with a target group indicated and asked to find the corresponding area of ridge detail in a second impression of the same finger and state when they found the target location. Target groups were presented on latent and plain exemplar fingerprint images, and as small areas cropped from the plain exemplars, to assess how image quality and the lack of surrounding visual context affected task performance and eye behavior. One hundred and seventeen participants completed a total of 675 trials. RESULTS: The presence or absence of context notably affected the areas viewed and time spent in comparison; differences between latent and plain exemplar tasks were much less significant. In virtually all trials, examiners repeatedly looked back and forth between the images, suggesting constraints on the capacity of visual working memory. On most trials where context was provided, examiners looked immediately at the corresponding location: with context, median time to find the corresponding location was less than 0.3 s (second fixation); however, without context, median time was 1.9 s (five fixations). A few trials resulted in errors in which the examiner did not find the correct target location. Basic gaze measures of overt behaviors, such as speed, areas visited, and back-and-forth behavior, were used in conjunction with the known target area to infer the underlying cognitive state of the examiner. CONCLUSIONS: Visual context has a significant effect on the eye behavior of latent print examiners. Localization errors suggest how errors may occur in real comparisons: examiners sometimes compare an incorrect but similar target group and do not continue to search for a better candidate target group. The analytic methods and predictive models developed here can be used to describe the more complex behavior involved in actual fingerprint comparisons.

The permanence of friction ridge skin and persistence of friction ridge skin and impressions: A comprehensive review and new results.

This study addresses the permanence and persistence of friction ridges and the persistence of impressions made from these friction ridges over months and years. Permanence is the unchanging presence and appearance of friction ridge arrangements and their attributes between recurring observations of the skin. Permanence was evaluated from direct photographs of fingers collected over a period of 30-45 days (covering one or more skin regeneration cycles) as well as after 8 or more years had elapsed. Persistence embodies the operational concept of whether or not a pair of images displays sufficient similarity upon which to base an informed decision that they were made by the same finger, while acknowledging certain dissimilarities or distortions due to friction ridge physiology, image capture, matrix, substrate, and applied pressure. Persistence applies to both friction ridge skin and impressions made from these friction ridges. Permanence and persistence of skin were assessed from direct photographs of fingers taken two months apart and from finger photographs separated by an interval of at least 8 years. Permanence and persistence were also assessed from impressions taken over 4 months, as well as those separated by 8-53 years. Variability due to capture method was assessed by using four image capture methods over a four month period: direct photography of fingers, impressions captured by ink, holographic imaging, and live scan. Qualified latent fingerprint examiners assessed all changes observed over time, as well as any limitations imposed by capture method. The practice of comparison and identification of fingerprint impressions was upheld, as was the prevailing use of the word persistence to describe stability of friction ridges. All photographs and impressions of the same finger were identifiable as originating from the same source. Within all the periods of observation, level 1 detail was permanent and persistent. Persistence, but not permanence, was supported for level 2 detail. Notably, the small changes observed were only in appearance; there were no changes in the presence of new, or absence of existing, minutiae. Level 3 details of ridge edge shape and pore presence were neither permanent nor persistent. Ridge width was permanent and persistent. Incipient ridges were neither permanent nor persistent.

Factors associated with latent fingerprint exclusion determinations.

Exclusion is the determination by a latent print examiner that two friction ridge impressions did not originate from the same source. The concept and terminology of exclusion vary among agencies. Much of the literature on latent print examination focuses on individualization, and much less attention has been paid to exclusion. This experimental study assesses the associations between a variety of factors and exclusion determinations. Although erroneous exclusions are more likely to occur on some images and for some examiners, they were widely distributed among images and examiners. Measurable factors found to be associated with exclusion rates include the quality of the latent, value determinations, analysis minutia count, comparison difficulty, and the presence of cores or deltas. An understanding of these associations will help explain the circumstances under which errors are more likely to occur and when determinations are less likely to be reproduced by other examiners; the results should also lead to improved effectiveness and efficiency of training and casework quality assurance. This research is intended to assist examiners in improving the examination process and provide information to the broader community regarding the accuracy, reliability, and implications of exclusion decisions.

Data on the interexaminer variation of minutia markup on latent fingerprints.

The data in this article supports the research paper entitled "Interexaminer variation of minutia markup on latent fingerprints" [1]. The data in this article describes the variability in minutia markup during both analysis of the latents and comparison between latents and exemplars. The data was collected in the "White Box Latent Print Examiner Study," in which each of 170 volunteer latent print examiners provided detailed markup documenting their examinations of latent-exemplar pairs of prints randomly assigned from a pool of 320 pairs. Each examiner examined 22 latent-exemplar pairs; an average of 12 examiners marked each latent.

Interexaminer variation of minutia markup on latent fingerprints.

Latent print examiners often differ in the number of minutiae they mark during analysis of a latent, and also during comparison of a latent with an exemplar. Differences in minutia counts understate interexaminer variability: examiners' markups may have similar minutia counts but differ greatly in which specific minutiae were marked. We assessed variability in minutia markup among 170 volunteer latent print examiners. Each provided detailed markup documenting their examinations of 22 latent-exemplar pairs of prints randomly assigned from a pool of 320 pairs. An average of 12 examiners marked each latent. The primary factors associated with minutia reproducibility were clarity, which regions of the prints examiners chose to mark, and agreement on value or comparison determinations. In clear areas (where the examiner was "certain of the location, presence, and absence of all minutiae"), median reproducibility was 82%; in unclear areas, median reproducibility was 46%. Differing interpretations regarding which regions should be marked (e.g., when there is ambiguity in the continuity of a print) contributed to variability in minutia markup: especially in unclear areas, marked minutiae were often far from the nearest minutia marked by a majority of examiners. Low reproducibility was also associated with differences in value or comparison determinations. Lack of standardization in minutia markup and unfamiliarity with test procedures presumably contribute to the variability we observed. We have identified factors accounting for interexaminer variability; implementing standards for detailed markup as part of documentation and focusing future training efforts on these factors may help to facilitate transparency and reduce subjectivity in the examination process.

Changes in latent fingerprint examiners' markup between analysis and comparison.

After the initial analysis of a latent print, an examiner will sometimes revise the assessment during comparison with an exemplar. Changes between analysis and comparison may indicate that the initial analysis of the latent was inadequate, or that confirmation bias may have affected the comparison. 170 volunteer latent print examiners, each randomly assigned 22 pairs of prints from a pool of 320 total pairs, provided detailed markup documenting their interpretations of the prints and the bases for their comparison conclusions. We describe changes in value assessments and markup of features and clarity. When examiners individualized, they almost always added or deleted minutiae (90.3% of individualizations); every examiner revised at least some markups. For inconclusive and exclusion determinations, changes were less common, and features were added more frequently when the image pair was mated (same source). Even when individualizations were based on eight or fewer corresponding minutiae, in most cases some of those minutiae had been added during comparison. One erroneous individualization was observed: the markup changes were notably extreme, and almost all of the corresponding minutiae had been added during comparison. Latents assessed to be of value for exclusion only (VEO) during analysis were often individualized when compared to a mated exemplar (26%); in our previous work, where examiners were not required to provide markup of features, VEO individualizations were much less common (1.8%).

A novel approach for latent print identification using accurate overlays to prioritize reference prints.

A novel approach to automated fingerprint matching and scoring that produces accurate locally and nonlinearly adjusted overlays of a latent print onto each reference print in a corpus is described. The technology, which addresses challenges inherent to latent prints, provides the latent print examiner with a prioritized ranking of candidate reference prints based on the overlays of the latent onto each candidate print. In addition to supporting current latent print comparison practices, this approach can make it possible to return a greater number of AFIS candidate prints because the ranked overlays provide a substantial starting point for latent-to-reference print comparison. To provide the image information required to create an accurate overlay of a latent print onto a reference print, "Ridge-Specific Markers" (RSMs), which correspond to short continuous segments of a ridge or furrow, are introduced. RSMs are reliably associated with any specific local section of a ridge or a furrow using the geometric information available from the image. Latent prints are commonly fragmentary, with reduced clarity and limited minutiae (i.e., ridge endings and bifurcations). Even in the absence of traditional minutiae, latent prints contain very important information in their ridges that permit automated matching using RSMs. No print orientation or information beyond the RSMs is required to generate the overlays. This automated process is applied to the 88 good quality latent prints in the NIST Special Database (SD) 27. Nonlinear overlays of each latent were produced onto all of the 88 reference prints in the NIST SD27. With fully automated processing, the true mate reference prints were ranked in the first candidate position for 80.7% of the latents tested, and 89.8% of the true mate reference prints ranked in the top ten positions. After manual post-processing of those latents for which the true mate reference print was not ranked first, these frequencies increased to 90.9% (1st rank) and 96.6% (top ten), respectively. Because the computational process is highly parallelizable, it is feasible for this method to work with a reference corpus of several thousand prints.

Measuring what latent fingerprint examiners consider sufficient information for individualization determinations.

Latent print examiners use their expertise to determine whether the information present in a comparison of two fingerprints (or palmprints) is sufficient to conclude that the prints were from the same source (individualization). When fingerprint evidence is presented in court, it is the examiner's determination--not an objective metric--that is presented. This study was designed to ascertain the factors that explain examiners' determinations of sufficiency for individualization. Volunteer latent print examiners (n = 170) were each assigned 22 pairs of latent and exemplar prints for examination, and annotated features, correspondence of features, and clarity. The 320 image pairs were selected specifically to control clarity and quantity of features. The predominant factor differentiating annotations associated with individualization and inconclusive determinations is the count of corresponding minutiae; other factors such as clarity provided minimal additional discriminative value. Examiners' counts of corresponding minutiae were strongly associated with their own determinations; however, due to substantial variation of both annotations and determinations among examiners, one examiner's annotation and determination on a given comparison is a relatively weak predictor of whether another examiner would individualize. The extensive variability in annotations also means that we must treat any individual examiner's minutia counts as interpretations of the (unknowable) information content of the prints: saying "the prints had N corresponding minutiae marked" is not the same as "the prints had N corresponding minutiae." More consistency in annotations, which could be achieved through standardization and training, should lead to process improvements and provide greater transparency in casework.

Understanding the sufficiency of information for latent fingerprint value determinations.

A latent print examiner's assessment of the value, or suitability, of a latent impression is the process of determining whether the impression has sufficient information to make a comparison. A "no value" determination preemptively states that no individualization or exclusion determination could be made using the impression, regardless of quality of the comparison prints. Factors contributing to a value determination include clarity and the types, quantity, and relationships of features. These assessments are made subjectively by individual examiners and may vary among examiners. We modeled the relationships between value determinations and feature annotations made by 21 certified latent print examiners on 1850 latent impressions. Minutia count was strongly associated with value determinations. None of the models resulted in a stronger intraexaminer association with "value for individualization" determinations than minutia count alone. The association between examiner annotation and value determinations is greatly limited by the lack of reproducibility of both annotation and value determinations.

Assessing the clarity of friction ridge impressions.

The ability of friction ridge examiners to correctly discern and make use of the ridges and associated features in finger or palm impressions is limited by clarity. The clarity of an impression relates to the examiner's confidence that the presence, absence, and attributes of features can be correctly discerned. Despite the importance of clarity in the examination process, there have not previously been standard methods for assessing clarity in friction ridge impressions. We introduce a process for annotation, analysis, and interchange of friction ridge clarity information that can be applied to latent or exemplar impressions. This paper: (1) describes a method for evaluating the clarity of friction ridge impressions by using color-coded annotations that can be used by examiners or automated systems; (2) discusses algorithms for overall clarity metrics based on manual or automated clarity annotation; and (3) defines a method of quantifying the correspondence of clarity when comparing a pair of friction ridge images, based on clarity annotation and resulting metrics. Different uses of this approach include examiner interchange of data, quality assurance, metrics, and as an aid in automated fingerprint matching.

Repeatability and reproducibility of decisions by latent fingerprint examiners.

The interpretation of forensic fingerprint evidence relies on the expertise of latent print examiners. We tested latent print examiners on the extent to which they reached consistent decisions. This study assessed intra-examiner repeatability by retesting 72 examiners on comparisons of latent and exemplar fingerprints, after an interval of approximately seven months; each examiner was reassigned 25 image pairs for comparison, out of total pool of 744 image pairs. We compare these repeatability results with reproducibility (inter-examiner) results derived from our previous study. Examiners repeated 89.1% of their individualization decisions, and 90.1% of their exclusion decisions; most of the changed decisions resulted in inconclusive decisions. Repeatability of comparison decisions (individualization, exclusion, inconclusive) was 90.0% for mated pairs, and 85.9% for nonmated pairs. Repeatability and reproducibility were notably lower for comparisons assessed by the examiners as "difficult" than for "easy" or "moderate" comparisons, indicating that examiners' assessments of difficulty may be useful for quality assurance. No false positive errors were repeated (n = 4); 30% of false negative errors were repeated. One percent of latent value decisions were completely reversed (no value even for exclusion vs. of value for individualization). Most of the inter- and intra-examiner variability concerned whether the examiners considered the information available to be sufficient to reach a conclusion; this variability was concentrated on specific image pairs such that repeatability and reproducibility were very high on some comparisons and very low on others. Much of the variability appears to be due to making categorical decisions in borderline cases.

Accuracy and reliability of forensic latent fingerprint decisions.

The interpretation of forensic fingerprint evidence relies on the expertise of latent print examiners. The National Research Council of the National Academies and the legal and forensic sciences communities have called for research to measure the accuracy and reliability of latent print examiners' decisions, a challenging and complex problem in need of systematic analysis. Our research is focused on the development of empirical approaches to studying this problem. Here, we report on the first large-scale study of the accuracy and reliability of latent print examiners' decisions, in which 169 latent print examiners each compared approximately 100 pairs of latent and exemplar fingerprints from a pool of 744 pairs. The fingerprints were selected to include a range of attributes and quality encountered in forensic casework, and to be comparable to searches of an automated fingerprint identification system containing more than 58 million subjects. This study evaluated examiners on key decision points in the fingerprint examination process; procedures used operationally include additional safeguards designed to minimize errors. Five examiners made false positive errors for an overall false positive rate of 0.1%. Eighty-five percent of examiners made at least one false negative error for an overall false negative rate of 7.5%. Independent examination of the same comparisons by different participants (analogous to blind verification) was found to detect all false positive errors and the majority of false negative errors in this study. Examiners frequently differed on whether fingerprints were suitable for reaching a conclusion.