Quantifying evidence in forensic authorship analysis


  • Tim Grant Aston University




forensic linguistics, , authorship analysis, error, sampling, discriminant analysis, bayes theorem


The judicial interest in ‘scientific’ evidence has driven recent work to quantify results for forensic linguistic authorship analysis. Through a methodological discussion and a worked example this paper examines the issues which complicate attempts to quantify results in work. The solution suggested to some of the difficulties is a sampling and testing strategy which helps to identify potentially useful, valid and reliable markers of authorship. An important feature of the sampling strategy is that these markers identified as being generally valid and reliable are retested for use in specific authorship analysis cases. The suggested approach for drawing quantified conclusions combines discriminant function analysis and Bayesian likelihood measures. The worked example starts with twenty comparison texts for each of three potential authors and then uses a progressively smaller comparison corpus, reducing to fifteen, ten, five and finally three texts per author. This worked example demonstrates how reducing the amount of data affects the way conclusions can be drawn. With greater numbers of reference texts quantified and safe attributions are shown to be possible, but as the number of reference texts reduces the analysis shows how the conclusion which should be reached is that no attribution can be made. The testing process at no point results in instances of a misattribution.

Author Biography

Tim Grant, Aston University

TIM GRANT has worked in the field of Forensic Authorship Analysis for more than 10 years and in 2005 received a PhD from the University of Birmingham in the field. He has worked across disciplines in psychology and linguistics departments and is now Senior Lecturer with special responsibility for Forensic Linguistics in the School of Languages and Social Sciences at Aston University. Currently, his main research interests are the language of interactions between offenders and victims in cases of sexual assault and rape and the language of text messaging.



How to Cite

Grant, T. (2007). Quantifying evidence in forensic authorship analysis. International Journal of Speech, Language and the Law, 14(1), 1–25. https://doi.org/10.1558/ijsll.v14i1.1