Cranial Nonmetric Sexual Dimorphism and Sex Estimation in East and Southeast Asian Individuals

Abstract

Sex—often analyzed through the visual assessment of robust or gracile nonmetric skeletal features—is one of the most important components of the biological profile, as it dictates the methods used in the estimation of age and stature. Differences in sexual dimorphism exist between populations; however, little work has tested the efficacy of nonmetric-scoring systems on Asian groups. This study examines cranial (nuchal crest, mastoid process, supraorbital margin, glabella, and mental eminence) nonmetric sexual dimorphism in 1,397 Japanese and Thai individuals through the development of population-specific univariate and multivariate statistics, which were subsequently tested on 109 Filipino individuals. The univariate sectioning points produced classification accuracies of 45.5–93.2%, while cross-validated logistic regression equations resulted in classification accuracies of 68.4–97.3%. However, Walker’s (2008) and Garvin et al.’s (2014) discriminant functions developed on non-Asian individuals produced lower classification accuracies and higher sex biases when applied to the Asian samples due to reduced sexual dimorphism. While some population differences exist between the Japanese and Thai, the inclusion of population in statistical models failed to contribute to the predictions. Further, the success of the univariate and multivariate models on the Filipino sample suggests that they can be cautiously applied to other East and Southeast Asian groups. While age and intraobserver error minimally affect the nonmetric traits, secular change may influence their expression, thereby complicating their use in sex estimation. The findings of this research underscore the importance of developing Asian-specific biological profile methods in the current judicial climate.