Handwriting Evidence Evaluation Based on the Shape of Characters: Application of Multivariate Likelihood Ratios

Authors


  • Presented in part at the 14th Conference of the International Graphonomics Society, September 13-16, 2009, in Dijon, France.

  • Supported by Research Grant n. K-11K1-116620 from the Swiss National Science Foundation.

Additional information and reprint requests:
Raymond Marquis, Ph.D.
Institut de Police Scientifique
School of Criminal Justice
Bâtiment Batochime
University of Lausanne
CH-1015 Lausanne-Dorigny
Switzerland
E-mail: raymond.marquis@unil.ch

Abstract

Abstract:  A novel Bayesian methodology has been developed to quantitatively assess handwriting evidence by means of a likelihood ratio (LR) designed for multivariate data. This methodology is presented and its applicability is shown through a simulated case of a threatening anonymous text where a suspect is apprehended. The shape of handwritten characters a, d, o, and q of the threatening text was compared with characters of the true writer, and then with two other writers, one with similar and one with dissimilar characters shape compared to the true writer. In each of these three situations, 100 draws of characters were made and the resulting distributions of LR were established to consider the natural handwriting variation. LR values supported the correct hypothesis in every case. This original Bayesian methodology provides a coherent and rigorous tool for the assessment of handwriting evidence, contributing undoubtedly to integrate the field of handwriting examination into science.

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