The Likelihood-Ratio Framework and Forensic Evidence in Court: A Response to R v T

Source abstract

In R v T the Court of Appeal concluded that the likelihood-ratio framework should not be used for the evaluation of evidence except ‘where there is a firm statistical base’. The present article argues that the court's opinion is based on misunderstandings of statistics and of the likelihood-ratio framework for the evaluation of evidence. The likelihood-ratio framework is a logical framework and not itself dependent on the use of objective measurements, databases and statistical models. The ruling is analysed from the perspective of the new paradigm for forensic-comparison science: the use of the likelihood-ratio framework for the evaluation of evidence; a strong preference for the use of objective measurements, databases representative of the relevant population, and statistical models; and empirical testing of the validity and reliability of the forensic-comparison system under conditions reflecting those of the case at trial.