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7th International Workshop on Digital Forensics and Incident Analysis (WDFIA 2012)
Title: A Forensic Text Comparison in SMS Messages: A Likelihood Ratio Approach with Lexical Features
Author(s): Shunichi Ishihara
Keywords: SMS messages, forensic text comparison, likelihood ratio, multivariate kernel density, log-likelihood-ratio cost, calibration
Abstract: Due to its convenience and low cost, short message service (SMS) has been a very popular medium of communication for quite some time. Unfortunately, however, SMS messages are sometimes used for reprehensible purposes, e.g. communication between drug dealers and buyers, or in illicit acts such as extortion, fraud, scams, hoaxes, and false reports of terrorist threats. In this study, we perform a likelihood-ratio-based forensic text comparison of SMS messages focusing on lexical features. The likelihood ratios (LRs) are calculated in Aitken and Lucyâ€™s (2004) multivariate kernel density procedure, and are calibrated. The validity of the system is assessed based on the magnitude of the LRs using the log-likelihood-ratio cost (Cllr). The strength of the derived LRs is graphically presented in Tippett plots. The results of the current study are compared with those of previous studies.
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