The use of the likelihood ratio for evaluative and investigative purposes in comparative forensic handwriting examination

This paper extends previous research and discussion on the use of multivariate continuous data, which are about to become more prevalent in forensic science. As an illustrative example, attention is drawn here on the area of comparative handwriting examinations. Multivariate continuous data can be obtained in this field by analysing the contour shape of loop characters through Fourier analysis. This methodology, based on existing research in this area, allows one describe in detail the morphology of character contours throughout a set of variables. This paper uses data collected from female and male writers to conduct a comparative analysis of likelihood ratio based evidence assessment procedures in both, evaluative and investigative proceedings. While the use of likelihood ratios in the former situation is now rather well established (typically, in order to discriminate between propositions of authorship of a given individual versus another, unknown individual), focus on the investigative setting still remains rather beyond considerations in practice. This paper seeks to highlight that investigative settings, too, can represent an area of application for which the likelihood ratio can offer a logical support. As an example, the inference of gender of the writer of an incriminated handwritten text is forwarded, analysed and discussed in this paper. The more general viewpoint according to which likelihood ratio analyses can be helpful for investigative proceedings is supported here through various simulations. These offer a characterisation of the robustness of the proposed likelihood ratio methodology.     

Individuality of handwriting

Motivated by several rulings in United States courts concerning expert testimony in general, and handwriting testimony in particular, we undertook a study to objectively validate the hypothesis that handwriting is individual. Handwriting samples of 1,500 individuals, representative of the U.S. population with respect to gender, age, ethnic groups, etc., were obtained. Analyzing differences in handwriting was done by using computer algorithms for extracting features from scanned images of handwriting. Attributes characteristic of the handwriting were obtained, e.g., line separation, slant, character shapes, etc. These attributes, which are a subset of attributes used by forensic document examiners (FDEs), were used to quantitatively establish individuality by using machine learning approaches. Using global attributes of handwriting and very few characters in the writing, the ability to determine the writer with a high degree of confidence was established. The work is a step towards providing scientific support for admitting handwriting evidence in court. The mathematical approach and the resulting software also have the promise of aiding the FDE.     

Competency for Chinese Handwriting and Signature Examination

Chinese characters had their root some 4000 years ago and, with the growth in population, are used by over 1.3 billion people worldwide today; it is inevitable that document examiners would encounter cases involving the examination of Chinese handwriting regardless of their location. Although there are extensive studies on the examination of English handwriting in the literature, similar studies on Chinese handwriting are relatively limited. We are seeking to explore the obstacles and challenges for a document examiner who is unfamiliar with Chinese characters to apply the principles of identification and elimination of authorship described in the literature to examine Chinese handwriting, and how can these document examiners demonstrate their competency for conducting Chinese handwriting examination. This study provides a review of the literature, compares the methodology and key features in English and Chinese handwriting examination, and describes various workshops and proficiency testing programs organized to assist document examiners seeking development in Chinese handwriting and signature examination.     

书写习惯未定型成年人笔迹检验

目的研究书写习惯未定型成年人笔迹的检验方法。方法通过实例研究分析成年人笔迹变化的特点和原因,确定笔迹性质和检验方法。结果书写习惯未定型也是成年人笔迹变化的重要原因。书写习惯未定型成年人笔迹是成年人正常笔迹的例外,适用正常笔迹检验方法。结论本研究确立了检材笔迹与样本笔迹非本质差异的判断标准,适用于短时间内变化较大的成年人笔迹的同一认定。     

浅谈左手书写者左右手笔迹的特点及变化规律

目的为左手书写者左手笔迹及右手笔迹的检验鉴定提供参考依据。方法收集左手书写者的左手正常笔迹和其右手笔迹,进行比对检验和实验数据统计分析。探讨左手书写者左手笔迹和右手笔迹的特点及变化规律。将左手书写者的左、右手笔迹的特点和变化规律与右手书写者的右、左手笔迹的特点和变化规律进行比较。结果左手书写者的左手笔迹和右手笔迹在笔顺、写法、错别字等特征上保持稳定。结论左手书写者的笔迹检验应结合其左手笔迹和右手笔迹的特点和变化规律,并注意其与右手书写者的右手笔迹和左手笔迹的特点和变化规律的区别与联系。     

On the discriminability of the handwriting of twins

As handwriting is influenced by physiology, training, and other behavioral factors, a study of the handwriting of twins can shed light on the individuality of handwriting. This paper describes the methodology and results of such a study where handwriting samples of twins were compared by an automatic handwriting verification system. The results complement that of a previous study where a diverse population was used. The present study involves samples of 206 pairs of twins, where each sample consisted of a page of handwriting. The verification task was to determine whether two half-page documents (where the original samples were divided into upper and lower halves) were written by the same individual. For twins there were 1236 verification cases -- including 824 tests where the textual content of writing was different, and 412 tests where it was the same. An additional set of 1648 test cases were obtained from handwriting samples of nontwins (general population). To make the handwriting comparison, the system computed macro features (overall pictorial attributes), micro features (characteristics of individual letters), and style features (characteristics of whole-word shapes and letter pairs). Four testing scenarios were evaluated: twins and nontwins writing the same text and writing different texts. Results of the verification tests show that the handwriting of twins is less discriminable than that of nontwins: an overall error rate of 12.91% for twins and 3.7% for nontwins. Error rates with identical twins were higher than with fraternal twins. Error rates in all cases can be arbitrarily reduced by rejecting (not making a decision on) borderline cases. A level of confidence in the results obtained is given by the fact that system error rates are comparable to that of humans (lower than that of lay persons and higher than that of questioned document examiners [QDEs]).     

Size influence on shape of handwritten characters loops

In the practice of forensic handwriting experts, the size of the writing on a questioned document may be different from that of known samples. In this study, the hypothesis of shape invariance of handwritten closed loops across size increasing was tested. A Fourier methodology was applied to 2325 small letters (591 a loops, 547 d loops, 596 o loops and 591 q loops) and 692 enlarged letters (162 a loops, 173 d loops, 173 o loops and 184 q loops), in a population of 13 writers who were asked to write letters in their usual size and about three times larger. Most of the writers presented similar modifications when increasing the size of the loops; they produced enlarged loops significantly more round and less slanted towards the right or the left. Furthermore, a discrimination was demonstrated between the writers on the basis of the enlarged loops, with a correct classification rate superior to 90%, whatever the letter (a, d, o or q). A classification of the enlarged loops in their corresponding writer was then possible. On the contrary, when comparing the enlarged loops to the small ones, almost one half of the enlarged loops were allocated to a wrong writer. Shape invariance was thus not supported for this particular application. Consequently, when comparing documents with a different writing size, differences in loops shape should be interpreted cautiously because they may be due to a different writer, but they may also be due to an enlargement of the loops. Therefore, reference material of similar writing size to that of the questioned writing should be requested for the comparison of handwritten loops.     

Handwriting of the alcoholic

Alcohol intoxication produces abnormal handwriting with manifestations that are thoroughly described in the literature of forensic science. A less known phenomenon is the peculiar handwriting changes found in alcoholics, especially individuals in the later stages of the disease. In addition to the two handwriting states of non-alcoholic drinkers (normal/sober and intoxicated) the alcoholic writer has a third state, handwriting done in withdrawal. Withdrawal is a state of tension resulting in handwriting characterized by irregularity, ataxia and tremor. This type of abnormal handwriting creates special problems of authentication requiring detailed background history and appropriate comparison specimens, but it can also be used to judge the writer's state of sobriety.     

Beyond traditional paternity and identification cases. Selecting the most probable pedigree

The paper extends on the traditional methodology used to quantify DNA evidence in paternity or identification cases. By extending we imply that there are more than two alternatives to choose between. In a standard paternity case the two competing explanations H(1): "John Doe is the father of the child and H(2): "A random man is the father of the child, are typically considered. A paternity index of 100000 implies that the data is 100000 more likely assuming hypothesis H(1) rather than H(2). If H(2) is replaced by "A brother of John Doe is the father", the LR may change dramatically. The main topic of this paper is to determine the most probable pedigree given a certain set of data including DNA profiles. In the previous example this corresponds to determining the most likely relation between John Doe and the child. Based on DNA obtained from victims of a fire, bodies found in an ancient grave or from individuals seeking to confirm their anticipated family relations, we would like to determine the most probable pedigree. The approach we present provides the possibility to combine non-DNA evidence, say age of individuals, and DNA profiles. The program familias, obtainable as shareware from http://www.nr.no/familias, delivers the probabilities for the various family constellations. More precisely, the information (if any) prior to DNA is combined with the DNA-profiles in a Bayesian manner to deliver the posterior probabilities. We exemplify using the well published Romanov data where the accepted solution emerges among 4536 possibilities considered. Various other applications based on forensic case work are discussed. In addition we have simulated data to resemble an incest case. Since the true family relation is known in this case, we may evaluate the method.     

Information‐Theoretical Assessment of the Performance of Likelihood Ratio Computation Methods

Performance of likelihood ratio (LR) methods for evidence evaluation has been represented in the past using, for example, Tippett plots. We propose empirical cross‐entropy (ECE) plots as a metric of accuracy based on the statistical theory of proper scoring rules, interpretable as information given by the evidence according to information theory, which quantify calibration of LR values. We present results with a case example using a glass database from real casework, comparing performance with both Tippett and ECE plots. We conclude that ECE plots allow clearer comparisons of LR methods than previous metrics, allowing a theoretical criterion to determine whether a given method should be used for evidence evaluation or not, which is an improvement over Tippett plots. A set of recommendations for the use of the proposed methodology by practitioners is also given.     

对一起右手食指缺损笔迹的检验

通过一起右手食指缺损笔迹的检验，研究执笔机理。对右手食指缺损后对其书写运动形式的影响、笔迹特点及检验时注意事项作了一些有益的探讨。     

A preliminary investigation into handwriting examination by multiple measurements of letters and spacing

Theoretically, the scientific measurement of letters, letter spacing and word spacing provides a mathematical basis for the statistical comparison of handwriting. Ten volunteers were asked to write the same short passage. Ten features were measured, up to 10 times each, to characterise each writer. Measurements of repeat handwriting 2 years later failed to identify the writer, and this was attributed to a change in the height of the middle zone. Measurements of 'it' and 'th' spacings were the least affected.     

Development of Individuality in Children's Handwriting

Handwriting of children in early grades is studied from the viewpoint of quantitatively measuring the development of handwriting individuality. Handwriting samples of children, in grades 2–4, writing a paragraph of text in both handprinted and cursive, collected over a period of 3 years, were analyzed using two different approaches: (i) characteristics of the word “and” and (ii) entire paragraphs using an automated system. In the first approach, word characteristics were analyzed using statistical measures. In the second approach, pairs of paragraphs were compared. Both types of analysis, single word and complete writing, led to the same conclusions: (i) handwriting of each child remains relatively similar when handwriting has been just learnt and becomes markedly different from grades 3 to 4 and (ii) handwriting of different children becomes progressively more different from grades 2 to 4. The results provide strong support that handwriting becomes more individualistic with child development.     

Alcohol: its effect on handwriting

A series of research studies was conducted to determine if there would be changes in the handwriting of 35 men and women after they had been drinking. Handwriting samples were taken before the participants had consumed any alcohol and again after the drinking period had ended. Deterioration in the handwriting was charted. Based on this study, the handwriting could not be used in any way to measure accurately the blood alcohol concentration of a writer. The results of the handwriting comparisons are discussed.     

论笔迹鉴定结论的证据效力——兼谈“世纪遗产争夺案”的笔迹鉴定

笔迹鉴定在现代诉讼中日益增多,因其鉴定多依赖于＂经验知识＂,不具有可验证的重复性,也无法接受实证的重复性检验,致使其在作为证据使用时存在一定的分歧,尤其是遗嘱笔迹因书写人死亡,其鉴定结果更富有争议。香港历经＂八年＂旷日持久的＂世纪遗产争夺案＂中的笔迹鉴定颇具典型意义。笔迹鉴定结论如何在法庭中出示以及法庭对有争议的笔迹鉴定结论如何采纳或者排除,既是一个理论问题,又是一个制度问题,还是一个价值选择问题。因此,对笔迹鉴定结论的研究与探讨成为司法鉴定制度和证据制度必须直面的带有现实意义的问题。     

Bayesian analysis of fingerprint, face and signature evidences with automatic biometric systems

The Bayesian approach provides a unified and logical framework for the analysis of evidence and to provide results in the form of likelihood ratios (LR) from the forensic laboratory to court. In this contribution we want to clarify how the biometric scientist or laboratory can adapt their conventional biometric systems or technologies to work according to this Bayesian approach. Forensic systems providing their results in the form of LR will be assessed through Tippett plots, which give a clear representation of the LR-based performance both for targets (the suspect is the author/source of the test pattern) and non-targets. However, the computation procedures of the LR values, especially with biometric evidences, are still an open issue. Reliable estimation techniques showing good generalization properties for the estimation of the between- and within-source variabilities of the test pattern are required, as variance restriction techniques in the within-source density estimation to stand for the variability of the source with the course of time. Fingerprint, face and on-line signature recognition systems will be adapted to work according to this Bayesian approach showing both the likelihood ratios range in each application and the adequacy of these biometric techniques to the daily forensic work.     

卧姿笔迹特征的实验研究

目的为卧姿笔迹鉴定提供识别和评断的参考依据。方法比较108个不同书写水平者的仰卧、左侧卧、右侧卧及俯卧笔迹与正常坐姿笔迹特征上的异同点,通过大量实验数据的统计分析,总结出卧姿笔迹特征及其变化规律,探讨可能的变化原因,并分析卧姿笔迹检验的要点。结果卧姿笔迹在字体、写法、错别字、笔顺、字间组合和单字的基本搭配比例等特征上较稳定。这些特征可作为本质特征使用。4种卧姿中,俯卧笔迹特征最稳定;书写水平高者笔迹特征也较稳定。结论卧姿笔迹鉴定应结合卧姿笔迹特征变化规律,准确判断笔迹的形成条件,去伪存真,做出科学的评断。