The Quantitative Classification of Hair Form and Its Application to the Forensic Comparison of Japanese Head Hair

Abstract

A method for expressing the hair form of Japanese head hair in the form of numerical data was investigated with regard to inter-individual comparisons, and the utility of the method was evaluated based on the screening of experimental evidential hair samples by cluster analysis.   The four characteristics used for the quantification of hair form included a basic characteristic (5 categories), an additional characteristic (4 categories) and 2 peculiar morphologies (3 categories). The hair forms of Japanese head hair were expressed by 448 combinations of these 12 categories. In addition, two numerical features were used as numerical data related to hair form as follows; the length and number of curves facing an assumed straight-line drawn between the tip and root ends of a hair image copied on the paper. This numerical feature was newly designed for this study.   For confirming the availability of hair form for a hair comparison, the inter-individual comparison of Japanese males was investigated by a discrimination analysis using 13 variables, 11 values obtained by quantification and 2 numerical features. Head hairs from Japanese males were classified with a high level of discrimination between 2 individuals based only on hair form. Since the screening of evidential hair samples was investigated by a cluster analysis using 13 variables, in an experimental model of 40 evidential hair samples derived as an extra hair sample from 8 individuals, hair samples from 8 individuals were successfully discriminated using a cluster analysis.   It was confirmed that a morphological examination represents an important tool for use in forensic hair comparison and that hair form is indispensable for interpreting the similarity of morphological features between known control hairs and evidential hairs.