Probabilistic evaluation of handwriting evidence: likelihood ratio for authorship |
| |
Authors: | Silvia Bozza Franco Taroni Raymond Marquis Matthieu Schmittbuhl |
| |
Institution: | University 'Ca' Foscari' of Venice, Italy; University of Lausanne, Switzerland; University of Strasbourg, France |
| |
Abstract: | Summary. The evaluation of handwritten characters that are selected from an anonymous letter and written material from a suspect is an open problem in forensic science. The individualization of handwriting is largely dependent on examiners who evaluate the characteristics in a qualitative and subjective way. Precise individual characterization of the shape of handwritten characters is possible through Fourier analysis: each handwritten character can be described through a set of variables such as the surface and harmonics as demonstrated by Marquis and co-workers in 2005. The assessment of the value of the evidence is performed through the derivation of a likelihood ratio for multivariate data. The methodology allows the forensic scientist to take into account the correlation between variables, and the non-constant variability within sources (i.e. individuals). Numerical procedures are implemented to handle the complexity and to compute the marginal likelihood under competing propositions. |
| |
Keywords: | Bayes's theorem Evaluation of evidence Forensic science Handwriting evidence Likelihood ratio Multivariate data |
|