An empirical estimate of the precision of likelihood ratios from a forensic-voice-comparison system

Abstract

An acoustic-phonetic forensic-voice-comparison system was constructed using the time-averaged formant values of tokens of 61 male Chinese speakers' /i/, /e/, and /a/ monophthongs as input. Likelihood ratios were calculated using a multivariate kernel density formula. A separate set of likelihood ratios was calculated for each vowel phoneme, and these were then fused and calibrated using linear logistic regression. The system was tested via cross-validation. The validity and reliability of the results were assessed using the log-likelihood-ratio-cost function (Cllr, a measure of accuracy) and an empirical estimate of the credible interval for the likelihood ratios from different-speaker comparisons (a measure of precision). The credible interval was calculated on the basis of two independent pairs of samples for each different-speaker comparison pair.