From facial images of different quality to score based LR.

A simple method is proposed to assess the quality of a trace facial image in the context of the facial recognition system used using the similarity scores with low quality different-source facial images, defined as the Confusion Score (CS). Methods are proposed to calculate the probability of finding the correct facial image in a database using low quality images for investigational purposes using the CS, as well as calculation of the Likelihood Ratio (LR) for comparison of low quality trace facial images with good quality reference facial images, based on the assessed CS of the trace image. Improvement of performance of an LR-system using training datasets stratified on CS over the use of pooled data is demonstrated. Examples of using the proposed approach in simulated case examples are presented.

A method for forensic gasoline comparison in fire debris samples: A numerical likelihood ratio system.

In many arson cases gasoline is used as a means to start the fire. In this paper results are presented for a likelihood-ratio (LR) system aimed at comparing gasoline traces from fire debris to a reference gasoline. The LR-system is able to deal with disturbing effects caused by burning and exposure to surroundings: pyrolysis products, preferential adsorption and evaporation. This paper focusses on the criminalistic and statistical aspects of the design of the LR-system, and presents results on performance of the LR-system. The details of trace gasoline recovery from fire debris will be presented in an accompanying paper. Validation and performance measures show that this system gives well-calibrated LRs for comparisons involving trace samples with a spread in quantity of gasoline, evaporation levels, and matrices that are typically encountered in casework. Rates of misleading evidence are less than 3.5%. We conclude that, despite limitations in experimental design, this LR-system can be useful to the comparison of gasoline profiles in casework practice.

Decision support for using mobile Rapid DNA analysis at the crime scene.

Mobile Rapid DNA technology is close to being incorporated into crime scene investigations, with the potential to identify a perpetrator within hours. However, the use of these techniques entails the risk of losing the sample and potential evidence, because the device not only consumes the inserted sample, it is also is less sensitive than traditional technologies used in forensic laboratories. Scene of Crime Officers (SoCOs) therefore will face a 'time/success rate trade-off' issue when making a decision to apply this technology. In this study we designed and experimentally tested a Decision Support System (DSS) for the use of Rapid DNA technologies based on Rational Decision Theory (RDT). In a vignette study, where SoCOs had to decide on the use of a Rapid DNA analysis device, participating SoCOs were assigned to either the control group (making decisions under standard conditions), the Success Rate (SR) group (making decisions with additional information on DNA success rates of traces), or the DSS group (making decisions supported by introduction to RDT, including information on DNA success rates of traces). This study provides positive evidence that a systematic approach for decision-making on using Rapid DNA analysis assists SoCOs in the decision to use the rapid device. The results demonstrated that participants using a DSS made different and more transparent decisions on the use of Rapid DNA analysis when different case characteristics were explicitly considered. In the DSS group the decision to apply Rapid DNA analysis was influenced by the factors "time pressure" and "trace characteristics" like DNA success rates. In the SR group, the decisions depended solely on the trace characteristics and in the control group the decisions did not show any systematic differences on crime type or trace characteristic. Guiding complex decisions on the use of Rapid DNA analyses with a DSS could be an important step towards the use of these devices at the crime scene.

Likelihood ratio methods for forensic comparison of evaporated gasoline residues.

In the investigation of arson, evidence connecting a suspect to the fire scene may be obtained by comparing the composition of ignitable liquid residues found at the crime scene to ignitable liquids found in possession of the suspect. Interpreting the result of such a comparison is hampered by processes at the crime scene that result in evaporation, matrix interference, and microbial degradation of the ignitable liquid. Most commonly, gasoline is used as a fire accelerant in arson. In the current scientific literature on gasoline comparison, classification studies are reported for unevaporated and evaporated gasoline residues. In these studies the goal is to discriminate between samples of several sources of gasoline, based on a chemical analysis. While in classification studies the focus is on discrimination of gasolines, for forensic purposes a likelihood ratio approach is more relevant. In this work, a first step is made towards the ultimate goal of obtaining numerical values for the strength of evidence for the inference of identity of source in gasoline comparisons. Three likelihood ratio methods are presented for the comparison of evaporated gasoline residues (up to 75% weight loss under laboratory conditions). Two methods based on distance functions and one multivariate method were developed. The performance of the three methods is characterized by rates of misleading evidence, an analysis of the calibration and an information theoretical analysis. The three methods show strong improvement of discrimination as compared with a completely uninformative method. The two distance functions perform better than the multivariate method, in terms of discrimination and rates of misleading evidence.

Single-family versus multi-family introductions.

The early success of plant introduction as a function of source material and habitat quality was tested in Arnica montana to determine whether different introduction strategies could affect plant viability of the introduced population. Plants originating from related (single-family introductions) and unrelated (multi-family introductions) individuals were introduced into undisturbed sites and into sites which were limed, turf cut, or both turf cut and limed. For four consecutive years, we analysed plant performance by measuring survival time, growth, and reproductive capacity. Introduction success was found to be strongly affected by habitat quality. Turf cutting in combination with additional liming significantly increased reproductive capacity and stimulated early flowering. To restore eutrophic and acidified soil conditions, turf cutting with additional liming prior to introduction is recommended. Furthermore, a significant effect of multi-family introductions was observed. Multi-family introductions showed higher introduction success compared to single-family introductions. Although the long-term effects of multi-family introductions will emerge after several generations, the preliminary results suggest multi-family introductions as the most successful introduction strategy.