The skill of a group of forensic document examiners in expressing handwriting and signature authorship and production process opinions

Abstract

Between March 1998 and June 2001, the six members of the New Zealand Police Document Examination Section completed six blind forensic handwriting and signature trials where the identity of the questioned writings were known by the experimenters but not by the document examiners. A total of 7494 opinions were expressed by the examiner group regarding the authorship of questioned handwriting and signature samples. Of these opinions, 2700 were correct, 11 were erroneous and 4783 were inconclusive. This translates into an overall raw error score of 0.1% of opinions, and a ‘called error’ score (one calculated by excluding the inconclusive data) of 0.4% of opinions. In addition, a total of 2982 opinions were expressed by the group on whether questioned signatures were the product of a simulation process. The group did not express any opinions that a simulated signature was the product of a genuine writing process, nor did the examiners express any opinions that a genuine signature was the product of a simulation process. Thus, for process opinions there was a zero error rate for the group. This paper overviews the individual and group opinion data associated with each of the trials. ‘The results provide significant support to the validity and strong probative value of the skill that has been claimed by this group of examiners.

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