Measuring the validity and reliability of forensic likelihood-ratio systems

There has been a great deal of concern recently about validity and reliability in forensic science. This paper reviews for a broad target audience metrics of validity and reliability (accuracy and precision) which have been applied in forensic voice comparison and which are potentially applicable in other branches of forensic science. The metric of validity is the log likelihood-ratio cost (C_llr), and the metric of reliability is an empirical estimate of credible intervals. A revised procedure for the calculation of credible intervals is introduced.