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Historically, morphometric standards used in forensic anthropology and bioarchaeology were derived from individuals of African and European descent, along with ancient Native Americans. However, it is unlikely that these standards can be accurately applied to modern Asian populations, and they may introduce error into biological profiles. Due to different population histories, it is hypothesized that ancient Native American and modern Thai individuals are morphometrically distinct. This study investigates the differences in sexual dimorphism between 102 Native American adults and 100 Thai individuals, 17 to 96 years old. A total of 30 cranial, 8 mandibular, and 58 postcranial measurements were compared between the two groups. Using independent t-tests, MANOVAs, univariate sectioning points, and linear discriminant functions, the Native American and Thai samples were found to be significantly different in the expression of sexual dimorphism for many elements. Further, measurements tested in Spradley and Jantz’s (2011) American Black and American White discriminant function equations produce correct classification biases of –91.0–100.0% and often fail to correctly classify Native American and Thai individuals. Therefore, the metric sex estimation methods developed on non-Asian populations do not adequately classify Native American and Thai individuals, thereby underscoring the importance of population-specific equations. The population-specific statistics developed for the Native Americans correctly classify 48.1–93.8% (univariate) and 70.8–94.1% (multivariate) of individuals, while those
developed for the Thai correctly classify 47.8–93.0% (univariate) and 63.2–100.0% (multivariate). The most discriminating elements are population dependent: the humerus, clavicle, and tibia work best for Native Americans, while the os coxa, ulna, and scapula perform best for Thai individuals.