Estimation of sex from cranial measurements in a Western Australian population

It is widely accepted that the most accurate statistical estimations of biological attributes in the human skeleton (e.g., sex, age and stature) are produced using population-specific standards. As we previously demonstrated that the application of foreign standards to Western Australian individuals results in an unacceptably large sex bias (females frequently misclassified), the need for population-specific standards is duly required and greatly overdue. We report here on the first morphometric cranial sexing standards formulated specifically for application in, and based on the statistical analysis of, contemporary Western Australian individuals. The primary aim is to investigate the nature of cranial sexual dimorphism in this population and outline a series of statistically robust standards suitable for estimating sex in the complete bone and/or associated diagnostic fragments. The sample analysed comprised multi-detector computed tomography cranial scans of 400 individuals equally distributed by sex. Following 3D volume rendering, 31 landmarks were acquired using OsiriX, from which a total of 18 linear inter-landmark measurements were calculated. Measurements were analysed using basic descriptive statistics and discriminant function analyses employing jackknife validations of classification results. All measurements (except frontal breadth and orbital height - Bonferroni corrected) are sexually dimorphic with sex differences explaining 3.5-48.9% of sample variance. Bizygomatic breadth and maximum length of the cranium and the cranial base contribute most significantly to sex discrimination; the maximum classification accuracy was 90%, with a -2.1% sex-bias. We conclude that the cranium is both highly dimorphic and a reliable bone for estimating sex in Western Australian individuals.