A comparison of statistical models for the analysis of complex forensic DNA profiles

Complex mixtures and LtDNA profiles are difficult to interpret. As yet there is no consensus within the forensic biology community as to how these profiles should be interpreted. This paper is a review of some of the current interpretation models, highlighting their weaknesses and strengths. It also discusses what a forensic biologist requires in an interpretation model and if this can be realistically executed under current justice systems.     

Bayesian networks and the value of the evidence for the forensic two-trace transfer problem*

Forensic scientists face increasingly complex inference problems for evaluating likelihood ratios (LRs) for an appropriate pair of propositions. Up to now, scientists and statisticians have derived LR formulae using an algebraic approach. However, this approach reaches its limits when addressing cases with an increasing number of variables and dependence relationships between these variables. In this study, we suggest using a graphical approach, based on the construction of Bayesian networks (BNs). We first construct a BN that captures the problem, and then deduce the expression for calculating the LR from this model to compare it with existing LR formulae. We illustrate this idea by applying it to the evaluation of an activity level LR in the context of the two-trace transfer problem. Our approach allows us to relax assumptions made in previous LR developments, produce a new LR formula for the two-trace transfer problem and generalize this scenario to n traces.     

False-negative probability in the SEM/EDS automated discovery of iGSR particles: A Bayesian approach

The automated search software integrated with a scanning electron microscope (SEM/EDS) has been the standard tool for detecting inorganic gunshot residues (iGSR) for several decades. The detection of these particles depends on various factors such as collection, preservation, contamination with organic matter, and the method for sample analysis. This article focuses on the influence of equipment resolution setup on the backscattered electron images of the sample. The pixel size of these images plays a crucial role in determining the detectability of iGSR particles, especially those with sizes close to the pixel size. In this study, we calculated the probability of missing all characteristic iGSR particles in a sample using an SEM/EDS automated search and how it depends on the image pixel resolution setup. We developed and validated an iGSR particle detection model that links particle size with equipment registers and applied it to 320 samples analyzed by a forensic science laboratory. Our results show that the probability of missing all characteristic iGSR particles due to their size is below 5% for pixel sizes below 0.32 μm². These findings indicate that pixel sizes as large as twice the one commonly used in laboratory casework, that is, 0.16 μm², are effective for initial sample scanning, yielding good detection rates of characteristic particles that could exponentially reduce laboratory workload.     

The impact of the principles of evidence interpretation on the structure and content of statements

The Forensic Science Service (FSS) has devoted appreciable effort to developing the application of the principles of evidence interpretation. Much of the work has been reported in previous papers in this journal, in particular those that develop a model for Case Assessment and Interpretation (CAI). The principles of interpretation are restated and the implications for structure and content of statements are described.     

A framework for estimating probability of a match in forensic bite mark identification

In forensic dentistry, a human expert typically does the comparison and identification based on bite marks. Unlike DNA analysis, however, there is no quantitative basis with which to assign a probability for this given match. This paper proposes a framework for empirically estimating the probability of such a bite mark match and reports on initial experimental results. The methodology involved collection of dental population data (3D dental casts and bite mark images), image analysis for quantitatively measuring the degree of match (based on chamfer distance), and performing a logistic regression analysis using the collected population data to estimate the probability of match from the calculated degree of match. The model correctly predicted 35 of the 42 matches and 585 of the 588 mismatches. The method also has potential for use in other forensic applications in which the assignment of quantitative probabilities is important.     

Quantitative evaluation of the results of digital forensic investigations: a review of progress

Unlike conventional forensics, digital forensics does not at present generally quantify the results of its investigations. It is suggested that digital forensics should aim to catch up with other forensic disciplines by using Bayesian and other numerical methodologies to quantify its investigations’ results. Assessing the plausibility of alternative hypotheses (or propositions, or claims) which explain how recovered digital evidence came to exist on a device could assist both the prosecution and the defence sides in criminal proceedings: helping the prosecution to decide whether to proceed to trial and helping defence lawyers to advise a defendant how to plead. This paper reviews some numerical approaches to the goal of quantifying the relative weights of individual items of digital evidence and the plausibility of hypotheses based on that evidence. The potential advantages enabling the construction of cost-effective digital forensic triage schemas are also outlined.

Key points

• The absence of quantified results from digital forensic investigations, unlike those of conventional forensics, is highlighted.
• A number of approaches towards quantitative evaluation of the results of digital forensic investigations are reviewed.
• The significant potential benefits accruing from such approaches are discussed.

     

A statistical analysis of successional patterns in carrion-arthropod assemblages: implications for forensic entomology and determination of the postmortem interval.

A set of statistical protocols is proposed for analyzing carrion-arthropod succession in forensic entomology investigations. A total of 23 carrion-arthropod data sets from temperate, tropical, desert, and coastal environments were assembled in a standard format and analyzed using randomization tests and methods derived from quantitative community ecology. The data were analyzed in three ways. First, patterns of arthropod visitation on nonhuman carcasses were analyzed in each of the 23 cases. Analysis revealed two groups of taxa: those that persist on the carcass over a single time interval (= nonreoccurring taxa, 80% of the taxa) and those that appear, leave, and reappear over time on the carcass (= reoccurring taxa, 20%). Reoccurring taxa, which can confound estimation of the postmortem interval (PMI), were found in 6 classes, 12 orders, and 29 taxonomic families of arthropods, including some forensically important taxa (for example, calliphorids, sarcophagids, histerids). The recognition that reoccurring taxa exist and that they are found in forensically important groups is an early step toward factoring in their potential importance in future entomological investigations. Second, temporal changes in the taxonomic composition of the carrion-arthropod community were studied by quantifying the degree of taxonomic similarity between pairwise combinations of time-specific samples of the succession. In 13 of the 18 illustrated cases, the midsuccessional samples, owing to their higher species richness, were taxonomically more similar to all other pairwise samples, on the average, than early and late successional samples which were poorer in species. Variability in taxonomic composition is the norm for most periods of the succession; however, in 17 of the 23 cases, some successional periods (particularly endpoint samples) revealed no changes in arthropod species composition (= matching sample-pairs). When applied to medicolegal cases, it is suggested that data sets with large fractions of matching sample-pairs should produce wider-ranging PMI estimates, on the average, than data sets with smaller fractions of matching sample-pairs. Third, Monte Carlo simulation was applied to each of the 23 assemblages to test specific hypotheses about community-wide patterns of arthropod visitation times on nonhuman carcasses. Simulation results revealed that arthropod residence times in the majority of cases (13 or 56%) followed a "clumped" succession model, whereas, the remaining 10 cases (44%) showed a more "uniform" spacing pattern of residence times on carcasses. Comparison of species accumulation curves for observed and simulated data further revealed that among the 13 "clumped" cases, most (9 or 69%) followed a "clumped, early" model (rather than "clumped, midterm" or "clumped, late" models).(ABSTRACT TRUNCATED AT 400 WORDS)     

An approach to dissecting the congenitally malformed heart in the forensic autopsy: the value of sequential segmental analysis.

The demonstration of congenital heart disease at autopsy necessitates the careful preservation and examination of the heart, the vessels, and their connections. Techniques preserving these connections and using a reproducible and systematic approach are preferred. The Rokitansky method of organ block dissection, in combination with a system of heart examination termed sequential segmental analysis, provides such an approach. This study is based on the examination of heart specimens accessioned into the Frank E. Sherman, M.D., and Cora C. Lenox, M.D., Heart Museum (containing approximately 2400 specimens) of the Pathology Department, Children's Hospital of Pittsburgh. Specimens received in consultation during a 25-year period from hospitals and coroners'/medical examiners' offices were examined, and the corresponding reports were reviewed. Of 46 total heart specimens examined (1975-1999), 29 (63%) were dissected properly or left intact for dissection at Children's Hospital of Pittsburgh, and 17 (37%) were incorrectly dissected for the demonstration of congenital heart disease. Of these 17 cases, 11 (24%) displayed dissection errors, which did not hinder a complete diagnosis, 3 cases (6.5%) had errors that enabled only an incomplete diagnosis, and in 3 cases (6.5%), no diagnosis of congenital heart disease could be made. Dissection mistakes and means of avoiding them are discussed. Review of medical and family history, external and internal examination, and a reproducible and sequential method of examining the heart and its connections enables documentation of even the most complex cardiovascular anomalies.     

A psychometric evaluation of the Defence Style Questionnaire-40 in a UK forensic patient population

Psychological defence mechanisms have been considered important personality processes in the onset, maintenance and recovery of mental disorders. More recently, their application to understanding presenting problems and as potential outcome indicators for forensic patients has been recommended. However, to date there have been no investigations into the reliability and factor structure of defence mechanism assessments for this population. The current study investigated the factor structure, internal consistency and test-retest reliability of the Defence Style Questionnaire-40 (DSQ) for 160 adult male UK forensic patients. The three-factor model of defences proposed by the DSQ-40 developers was not confirmed in the study sample. Reliability indices of the three factors indicated that the Immature factor was the most ‘acceptable’ in terms of internal consistency. Test-retest reliability coefficients ranged from .70 to .91. A revised three-factor structure that closely corresponds to the original validation study is recommended following an exploratory factor analysis. The findings are compared with previous reliability and factor analytic evaluations of the DSQ-40, and recommendations for its use with forensic patients are discussed.     

Estimating the probability of allelic drop-out of STR alleles in forensic genetics

In crime cases with available DNA evidence, the amount of DNA is often sparse due to the setting of the crime. In such cases, allelic drop-out of one or more true alleles in STR typing is possible. We present a statistical model for estimating the per locus and overall probability of allelic drop-out using the results of all STR loci in the case sample as reference. The methodology of logistic regression is appropriate for this analysis, and we demonstrate how to incorporate this in a forensic genetic framework.     

A multivariate statistical approach to for the evaluation of the biogeographical ancestry information from traditional STRs

The capability to achieve biogeographic ancestry (BGA) information from DNA profiles have been largely explored in forensic genetics because of its potential usefulness in providing investigative clues. For law enforcement and security purposes, when genetic data have been obtained from unknown evidence, but no reference samples are available and no hints come out from DNA databases, it would be extremely useful at least to infer the ethno-geographic origin of the stain donor by just examining traditional STRs DNA profiles.Current protocols for ethnic origin estimation using STRs profiles are usually based on Principal Component Analysis approaches and Bayesian methods. The present study provides an alternative approach that involves the use of target multivariate data analysis strategies for estimation of the BGA information from unknown biological traces. A powerful multivariate technique such as Partial Least Squares-Discriminant Analysis (PLS-DA) has been applied on NIST U.S. population datasets containing, for instance, the allele frequencies of African-American, Asian, Caucasian and Hispanic individuals. PLS-DA approach provided robust classifications, yielding high sensitivity and specificity models capable of discriminating the populations on ethnic basis. Finally, a real casework has been examined by extending the developed model to smaller and more geographically-restricted populations involving, for instance, Albanian, Italian and Montenegrian individuals.     

重新认识中国传统“小说”概念的演变

中国古代小说研究虽已取得大量成果,但一直存在着一个概念混淆的问题,即把古代指称一些自由写作文体的"小说"与后来称呼通俗叙事的"小说"混为一谈.然而在古代的文学观念中,这两种文体具有不同的艺术和文化特征.因此这种混同造成了对中国文学发展历史和文体特征认识的模糊.     

论明末科举文风的文学效应

明代末年以研讨八股文兼及诗文创作的文社大量兴起,明末文学家大多经过文社的培养而享誉文坛,社团文人成为文坛的主要文人群体.作为备科举考试的社团文人,在社团内接受科举考试训练和八股文创作的学习,同时又从事诗文创作.社团文人的科举思维对他们的诗文创作具有深刻影响,形成明末文坛以六经为根柢的儒者古文.社团文人创作往往借鉴时文法入古文,或者借鉴古文法入时文,使明末文学创作与理论批评具有不同以往的鲜明特色.     

Simultaneous determination of eight catechins and four theaflavins in bottled tea by liquid chromatography-tandem mass spectrometry for forensic analysis

Tea, and particularly bottled tea, is widely consumed worldwide and is often encountered at crime scenes in poisoning cases or used in place of urine in drug abuse monitoring. Tea is a rich source of polyphenols, such as catechins and theaflavins, and these compounds are useful for identification of trace quantities of tea samples. However, information on the contents of catechins and theaflavins in bottled tea is limited. In this study, a method was developed for simultaneous analysis of eight catechins and four theaflavins in tea using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The concentrations of these polyphenols were determined in bottled black, oolong, and green teas after a simple pretreatment process by the standard addition method. The developed LC-MS/MS method was rapid and all tested polyphenol compounds were separated within ~14 min. All tea types contained all the catechins, at varying concentrations, but not all the theaflavins were present in all the tea types. This indicates that the theaflavin composition reflects the degree of the fermentation and could be used for discrimination among different types of tea. All the green tea samples contained all eight catechins; however, the concentrations of these compounds varied among the tea samples. Principal component analysis and hierarchical cluster analysis were useful for discrimination of samples. It has been unclear whether the variations of chemical components are useful for forensic discrimination. Our results demonstrate that, in addition to identification of tea varieties, catechins and theaflavins can be used for the discrimination of bottled tea samples.     

A study of the performance and utility of annealing in forensic glass analysis

The use of annealing in forensic glass casework is reviewed. New data is presented that suggests a continuous approach to the interpretation of such data may be superior to the classification approach. Data are presented supporting the previously observed relationship between change in refractive index (RI) and the thickness of the glass pane. An examination of the possible assumption of independence between RI and change in RI is undertaken.     

The use of error rates to predict and characterize the efficacy of presumptive field tests

From a forensic perspective, a presumptive test, one which indicates the presence or absence of a certain target material such as blood, is an invaluable tool. Among these tests, there are different specificities, sensitivities, and shelf lives. The accuracy of a test is an algebraic combination of the specificity and sensitivity of the test. Each test has limitations as given by its false positive and false negative rates. The aim of this study was to illustrate how the false positive and false negative rates are to be properly determined using a simulation study for the phenolphthalein test. New presumptive tests must be properly evaluated/validated through testing of commonly encountered household items and other potentially probative items usually found at crime scenes, however, the makeup of test sets must appropriately capture all error rates. In order to correctly use these results when the test is applied to an unknown sample recovered at a crime scene, the error rates cannot be applied directly to estimate whether or not the sample is actually the analyte of interest. In a validation study, the forensic scientist calculates the false positive rate as the p(Positive Reaction|Blood), whereas at the scene, the crime scene investigator wishes to determine the p(Blood|Positive Reaction). All crime scene investigators need to ensure that the conditional is not transposed when interpreting such results. Furthermore, this work provides a model for the assessment of a multiple test diagnostic system intended for investigators.     

A convergence approach to the analysis of political corruption: A cross-national study

A convergence approach to the analysis of country-level political corruptionis proposed based on Cohen and Felson's routine activities theory of crimeand Ades and Di Tells's tripartite analysis of corruption. It argues thatalthough structural incentives, risky policies, and the lack of effectiveinstitutional guardians independently contribute to the causation ofcorruption, their convergence in time and space creates opportunities forwidespread and systematic corruption. Structural incentives are stableeconomic and cultural conditions and include economic hardships,particularism, and history of political unaccountability. Risky policiesencompass monopolistic and interventionist practices by the government inthe production, distribution, and consumption of goods and services.Institutional guardians refer to the judiciary, the press, opposition partiesand the civil society that monitor officials' behavior. Data from 99countries and territories are used to evaluate hypotheses derived from thetheory. Findings lend strong support to the proposed formal propositions.It is also suggested that useful schemes for corruption diagnosis and reformcan be developed from the theory.