The application of traditional and geometric morphometric analyses for forensic quantification of sexual dimorphism: preliminary investigations in a Western Australian population

A current limitation of forensic practice in Western Australia is a lack of contemporary population-specific standards for biological profiling; this directly relates to the unavailability of documented human skeletal collections. With rapidly advancing technology, however, it is now possible to acquire accurate skeletal measurements from 3D scans contained in medical databases. The purpose of the present study, therefore, is to explore the accuracy of using cranial form to predict sex in adult Australians. Both traditional and geometric morphometric methods are applied to data derived from 3D landmarks acquired in CT-reconstructed crania. The sample comprises multi-detector computed tomography scans of 200 adult individuals; following 3D volume rendering, 46 anatomical landmarks are acquired using OsiriX (version 3.9). Centroid size and shape (first 20 PCs of the Procrustes coordinates) and the inter-landmark (ILD) distances between all possible pairs of landmarks are then calculated. Sex classification effectiveness of the 3D multivariate descriptors of size and shape and selected ILD measurements are assessed and compared; robustness of findings is explored using resampling statistics. Cranial shape and size and the ILD measurements are sexually dimorphic and explain 3.2 to 54.3 % of sample variance; sex classification accuracy is 83.5–88.0 %. Sex estimation using 3D shape appears to have some advantages compared to approaches using size measurements. We have, however, identified a simple and biologically meaningful single non-traditional linear measurement (glabella–zygion) that classifies Western Australian individuals according to sex with a high degree of expected accuracy (87.5–88 %).