Cranial and post cranial metric sex estimation in modern Thai and Native American individuals

Historically, metric and morphological standards used in forensic anthropology and bioarcheology were derived from individuals of European and African descent and ancient Native Americans. However, it is unlikely that these standards can be accurately applied to modern Asian populations. Due to different population histories, it is hypothesized that ancient Native American and modern Thai individuals are metrically distinct. This study investigates the metric differences in sexual dimorphism between 102 Native American (American Museum of Natural History) and 100 modern Thai (Khon Kaen University) individuals 17 to 96 years of age. A total of 28 cranial, 9 mandibular and 58 postcranial measurements were compared between Native American and Thai individuals. Subsequently, select measurements were tested in Spradley and Jantz's (2011) American Black and White sex estimation equations to see how equations derived from non-Asian populations perform on Native American and Thai individuals and to ascertain if population differences exist in the expression of sexual dimorphism. Lastly, population-specific logistic regression equations were developed for both sample populations. Using logistic regression equations and discriminant function analyses - quasi-ordinary least squares, the Native American and Thai groups are significantly different in the expression of sexual dimorphism. Further, Spradley and Jantz's (2011) equations often fail to correctly classify Native American and Thai individuals. In particular, the equations derived from American Black and White individuals frequently classified modern Thai and Native American males as females. Conversely, three American White equations and eight American Black equations classified more females as males for both populations. Therefore, the metric sex estimation methods developed on non-Asian populations do not adequately classify Native American and Thai individuals. The application of sex estimation methods developed on non-Asian populations results in reduced discriminatory power because Native Americans and Thais are less sexually dimorphic than African and European American individuals. The equations developed on the modern Thai sample correctly classified 71.1 - 96.0% of the individuals, while those developed on the Native American samples correctly 78.1 - 97.8%