Statistical Analysis in Forensic Science: Evidential Values of Multivariate Physicochemical Data

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Physicochemical data obtained in forensic science laboratories

1.1 Introduction

Various materials can be subjected to physicochemical examination by forensic experts. Such materials include illegal substances, blood and other body fluids, and transfer evidence (e.g. small fragments of glass, paint, fibres, plastics, organic and inorganic gunshot residues, fire debris). The size of samples subjected to analysis is very small, for example, fragments of glass with a linear dimension below 0.5 mm. Therefore, the analysis of morphological features, such as thickness and colour, is of no value for solving a comparison (Chapter 4) or classification problem (Chapter 5). Thus, it is necessary to employ the physicochemical features of the analysed fragments. When choosing an analytical method for analysis of microtraces for forensic purposes an expert should take into account not only the fact that the amount of material is very small but also that the method chosen should be non-destructive, leaving the material available for reuse. Examinations performed by the application of various analytical methods return several kinds of information including:

• qualitative data, for example, information on compounds detected in fire debris samples based on a chromatogram, information obtained from the spectrum of an unknown sample, and morphological information such as the number and thicknesses of layers in a cross-section of car paints;
• quantitative data, for example, the concentration of elements ...