Christopher Anderson
 | Name: Christopher Anderson Course: MSc;STAT Department: Department of Statistics Staff Supervisor: Julian Leslie Associate Supervisor: Andrzej Kozek Email Address: canderso@efs.mq.edu.au Thesis Title The Importance of Line Width Measurements in Discriminating between Pencil Types in Forensic Handwriting Investigations |
Abstract
The primary research question of my study is to determine whether the maximum line width measurements produced by different mechanical or propelling pencils provide a reliable method to discriminate between them. The motivation for this study arose from an actual case in which I was involved, where it was alleged that some pencil entries written in a diary were suspected of being added at a later time. It was claimed that the writer of these entries habitually wrote with a mechanical pencil. A statistical analysis comparing the measurements of the maximum line width of the suspect and substantively written pencil entries indicated that there was no difference between the mean line width of the suspect pencil entries and the mean line width of the substantively written entries. This result inferred that the pencil entries could have come from the same or a similar diameter pencil.
No meaningful research has been undertaken of any type on the physical and chemical characteristics of mechanical pencils in a forensic context on which to gauge the significance or otherwise of this result. Hence, there is a need for relatively simple non-destructive and cost effective testing that may assist the forensic document examiner (FDE) to distinguish between the artefacts produced by mechanical and wooden cased lead pencils. If such tests were available then they would be of significant value and perhaps in some matters negate the need for an elemental examination using a Scanning Electron Microscope that is costly, time consuming and to some extent destructive to the document.
I have undertaken a pilot study assessing the maximum line width of different mechanical pencils using a limited population to assess whether an in-depth study is warranted. The data obtained was modelled using a GLM. This analysis suggested the method is useful in discriminating between mechanical pencils of different lead diameters and different hardness or softness but further research needs to be undertaken to properly assess these bounds and to correctly analyse the variance so it can be tabulated in a manner that is useful to a FDE in their casework.
The pilot study further revealed that the line measurements might provide useful information about the average angle at which a person holds the writing instrument and the hand they use to write with. This information, if reliable, will assist the FDE not only in discriminating between different types of pencils but also provide an objective method to support the FDE conclusions on whether the writing under examination is of common authorship or the product of different authorship.