The value of scientific evidence for forensic multivariate data

Multivariate continuous data are becoming more prevalent in forensic science. Available databases may present a complex dependence structure, with several variables and several levels of variation. The assessment of the value of evidence can be performed by the derivation of a likelihood ratio, a rigorous concept that measures the change produced by a given item of information in the odds in favour of a proposition as opposed to another, when going from the prior to the posterior distribution. The derivation of a likelihood ratio may be a demanding task, essentially because of the complexity of the scenario at hand and the possible poor information at the forensic examiner’s disposal. This opened the door in the forensic community to a large debate about what should be the most appropriate way to take charge of uncertainty while presenting expressions of evidential value at trial. These ideas will be illustrated with reference to a comparative handwriting scenario.