J.A. Lambert

A model for case assessment and interpretation

The authors describe a new approach to decision-making in an operational forensic science organization based on a model, embodying the principles of Bayesian inference, which has been developed through workshops run within the Forensic Science Service for forensic science practitioners. Issues which arise from the idea of pre-assessment of cases are explored by means of a case example.

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.

More on the hierarchy of propositions: exploring the distinction between explanations and propositions

Interpretation of the weight of scientific evidence depends upon the framing of at least two competing propositions to weigh against each other. It is the stage of framing propositions that is the most difficult aspect of evidence interpretation. The logical structure for case assessment and interpretation has been described by the authors in three previous papers [Cook R, et al. A model for case assessment and interpretation. Science & Justice 1998; 38: 151-156. Cook R, et al. A hierarchy of propositions: deciding which level to address in casework. Science & Justice 1998; 38: 231-239. Cook R, et al. Case pre-assessment and review in a two-way transfer case. Science & Justice 1999; 39: 103-111]. This paper considers the framing of propositions in greater detail, in particular the intermediate stage of exploring less formal explanations. All of the discussion is based on experiences encountered in workshops with caseworking forensic scientists.

Taking Account of Peak Areas when Interpreting Mixed DNA Profiles

This paper establishes a logical framework for taking account of peak areas when interpreting mixed DNA STR profiles. The principles apply wherever such data are available but they are illustrated here by means of data which have been collected from made up mixtures of known concentrations analyzed at short tandem repeat loci. The data have led to some modeling assumptions which are used for numerical examples. In actual casework the proportions of the various components will not be known and there is a discussion of whether they should be allowed for by integrating over a prior distribution. This is a conceptual paper, rather than a prescription for casework, and the scope for further work is outlined.

STATISTICAL ANALYSIS OF DATA FOR THREE BRITISH ETHNIC GROUPS FROM A NEW STR MULTIPLEX

Data have been collected from 602 Caucasians, 190 Afro-Caribbeans and 257 Asians of Indo/Pakistani descent who have been profiled using a new six locus short tandem repeat (STR) multiplex. The data have been analysed by conventional significance testing methods: the exact test, homozygosity, and conventional goodness of fit to Hardy-Weinberg proportions. Frequency tables are given and the expected performance in British forensic casework is discussed.

A Bayesian approach to interpreting footwear marks in forensic casework

This paper describes an attempt to formalise the interpretation of footwear marks. First, the definitions of identification and individualisation which were given by Kirk are discussed and formalised, then a Bayesian analysis is presented in which the assumptions made are clarified. The analvsis is broken down into comnonents which reflect different interpretative issues. Application of a formal expression for the likelihood ratio is then illustrated by means of examples from casework in New Zealand and the United Kingdom.

Regional genetic variation in Caucasians.

When evaluating DNA evidence, the necessary calculations are often carried out using databases drawn from broad populations; for example, the Forensic Science Service (FSS) maintains genetic databases for the 3 major racial groups of England and Wales--Caucasian, Afro-Caribbean and Asian (from the Indian subcontinent). The resulting figures may be challenged in court on the premise that they are not based on data from the population of most relevance in the particular case under consideration. One important factor might be the location of the crime. Since the recent establishment of a National DNA Intelligence Database, data have been made available from a wide range of geographical regions in England and Wales. This paper gives details of analyses conducted to measure the differentiation between white caucasian populations from these regions and from other areas of the UK and abroad using a Bayesian approach.

Genetic differentiation within and between four UK ethnic groups

In previous papers [L.A. Foreman, J.A. Lambert, I.W. Evett, Regional genetic variation in Caucasians, Forensic Sci. Int. 95 (1998) 27-37; L.A. Foreman, Analyses to investigate appropriate measures of differentiation between European Caucasian populations using short tandem repeat (STR) data, FSS Research Report FSS-RR-804 (1999)], we have carried out detailed investigations of the level of regional and national variation in STR characteristics exhibited within white Caucasian populations. The studies described here extend our earlier work to the black African/Caribbean and Asian (Indo-Pakistani) populations of the UK, routinely considered in casework calculations at the Forensic Science Service (FSS). In addition, estimation of allele distributions and database comparisons are carried out for two further populations, i.e. those classified as containing individuals of Oriental and Arabic appearance.

The refractive index distribution of control glass samples examined by the Forensic Science Laboratories in the United Kingdom

Abstract For several years the laboratories of the Home Office Forensic Science Service and the Metropolitan Police Forensic Science Laboratory have been pooling the data that they collect from carrying out refractive index measurements on control glass samples submitted for examination in routine casework. The data are all stored on a computer at the Central Research Establishment and they can be searched by operational scientists directly from terminals in their own laboratories. This paper describes the system, presents the data and summarises the salient features.

STATISTICAL ANALYSIS OF A LARGE FILE OF DATA FROM STR PROFILES OF BRITISH CAUCASIANS TO SUPPORT FORENSIC CASEWORK

Data from nearly 2500 British Caucasians, profiled using an STR quadruplex, have been analysed. The data came from several laboratories and represent samples from different geographical distributions. Analysis of the combined files shows that previous reports of failed independence tests were the results of sampling effects. A further convincing proof is given of the robustness of the statistical methods used to estimate evidential value in case-work. Comparisons between different samples show that regional effects between Scotland and the South of England have no importance from the forensic viewpoint.