Advanced measurement methods in forensic handwriting examination

The geometric-structural examination method assumes that the structure of a signature or handwritten entry can be described using geometric figures defined by characteristic points in the handwriting. These points are treated as the vertices of figures constructed over the signature or text fragment being analysed.

Unlike Brosson’s earlier geometric projection method, in which the construction points were strictly defined, the geometric figures method allows their number and position to be adapted to the individual structure of the signature being analysed. A methodological requirement remains, however, to use identical reference points in the questioned material and the reference material, eliminating the possibility of arbitrary interpretation during the analysis.

Examination practice uses various configurations of geometric figures, including:

• determining the signature’s dimensions by identifying its outermost points,
• creating angular arrangements defining the directions of the writing line,
• constructing triangles and quadrilaterals describing relationships between signature elements,
• building more complex polygons encompassing a greater number of characteristic points.

The analysis then compares the shape and proportions of the figures constructed in the questioned material and reference material. Correspondence between these geometric structures may indicate identity, whereas significant differences may suggest that the signatures were made by different people.

However, the literature emphasises that this method’s principal advantage is its strong illustrative value. Diagrams of geometric figures can clearly illustrate the results of the analysis and make them easier for the procedural authority and parties to the proceedings to understand. At the same time, it is noted that this method rarely provides an independent basis for identification conclusions and should be treated as an aid to classical graphical comparison analysis (Całkiewicz, 2009).

The statistical verification method for examination material attempts to introduce elements of probability theory into handwriting identification. Its aim is not to replace the traditional graphic comparative method, but to provide a statistical interpretation of the results obtained during that analysis.

The essence of this method is to determine how frequently individual handwriting features occur in a defined population of writers. Such data could be used to estimate the probability that a particular set of handwriting features might arise independently in two different people.

If the probability of the analysed combination of features recurring in the population were very low, the expert could conclude that there was a high probability of common authorship of the two entries. If that probability were greater, the opinion’s conclusions would have to be probabilistic in nature.

This method has significant methodological advantages because it allows the opinion’s conclusions to be based on objective statistical calculations. At the same time, its use faces serious practical limitations. Above all, it requires extensive statistical research on the frequency of individual handwriting features in a given population, which has not been carried out comprehensively in many countries, including Poland.

It is also noted that this method is unsuitable for analysing short texts or most signatures, or where handwriting has been deliberately distorted or produced in unusual conditions. For these reasons, its use in expert opinion practice remains limited (Całkiewicz, 2009).

The method for calculating the handwriting integration coefficient was proposed by Antoni Feluś as an attempt to describe the graphic structure of handwriting quantitatively. Its author proposed moving away from the traditional concept of a writing impulse, which in handwriting examination refers to the number of letters or writing elements produced without lifting the writing instrument from the surface.

According to Feluś, the concept of an impulse is too general to define handwriting structure precisely. The measurable category of handwriting integration level was proposed in its place, allowing more precise analysis of the connections between writing elements.

The level of handwriting integration is expressed by a mathematical coefficient defining the ratio of connected handwriting elements to elements that remain separate. The coefficient is expressed by the formula:

I = w / nw

where:

• I – handwriting integration level,
• w – number of interconnected handwriting elements,
• nw —the number of handwriting elements that remain unconnected.

The higher the integration coefficient, the more connected the handwriting elements and the more compact its structure. Lower values indicate more fragmented writing.

The method therefore allows the structure of handwriting to be characterised quantitatively and can be used in comparative analysis of different handwriting samples. As with other statistical methods, however, its practical use requires a sufficiently extensive body of examination material and a careful measurement procedure (Feluś, 1991).