A Decision Tree for Nonmetric Sex Assessment from the Skull

This study uses five well‐documented cranial nonmetric traits (glabella, mastoid process, mental eminence, supraorbital margin, and nuchal crest) and one additional trait (zygomatic extension) to develop a validated decision tree for sex assessment. The decision tree was built and cross‐validated on a sample of 293 U.S. White individuals from the William M. Bass Donated Skeletal Collection. Ordinal scores from the six traits were analyzed using the partition modeling option in JMP Pro 12. A holdout sample of 50 skulls was used to test the model. The most accurate decision tree includes three variables: glabella, zygomatic extension, and mastoid process. This decision tree yielded 93.5% accuracy on the training sample, 94% on the cross‐validated sample, and 96% on a holdout validation sample. Linear weighted kappa statistics indicate acceptable agreement among observers for these variables. Mental eminence should be avoided, and definitions and figures should be referenced carefully to score nonmetric traits.     

Reliability of the Walker Cranial Nonmetric Method and Implications for Sex Estimation

The cranial trait scoring method presented in Buikstra and Ubelaker (Standards for data collection from human skeletal remains. Fayetteville, AR: Arkansas Archeological Survey Research Series No. 44, 1994) and Walker (Am J Phys Anthropol, 136, 2008 and 39) is the most common nonmetric cranial sex estimation method utilized by physical and forensic anthropologists. As such, the reliability and accuracy of the method is vital to ensure its validity in forensic applications. In this study, inter‐ and intra‐observer error rates for the Walker scoring method were calculated using a sample of U.S. White and Black individuals (n = 135). Cohen's weighted kappas, intraclass correlation coefficients, and percentage agreements indicate good agreement between trials and observers for all traits except the mental eminence. Slight disagreement in scoring, however, was found to impact sex classifications, leading to lower accuracy rates than those published by Walker. Furthermore, experience does appear to impact trait scoring and sex classification. The use of revised population‐specific equations that avoid the mental eminence is highly recommended to minimize the potential for misclassifications.     

Metric Assessment of the Pubic Bone Using Known and Novel Data Points for Sex Estimation,

Biological sex estimation of skeletal remains is essential in forensic and archaeological analyses. Anthropologists most often use the pelvis, which is the most sexually dimorphic element both morphologically and metrically. While nonmetric pubic bone features have been studied extensively, few metric studies have examined this individual bone for dimorphism. For this study, three observers examined three previously identified and ten novel measurements of the pubic body on a modern sample of isolated pubic bones from the Maricopa County Forensic Science Center (FSC), in Phoenix, Arizona (n = 400). A relationship between pubic body measurements and biological sex was demonstrated, with significant correlations. Discriminant function analyses found that five measurements, four of which were novel, discriminated between males (89%) and females (86%). Observer experience level did not significantly impact the results. These five measurements were reliable and show promise for inclusion in metric methods for assessment of sex.     

Metric Sex Determination of the Human Coxal Bone on a Virtual Sample using Decision Trees

Decision trees provide an alternative to multivariate discriminant analysis, which is still the most commonly used in anthropometric studies. Our study analyzed the metric characterization of a recent virtual sample of 113 coxal bones using decision trees for sex determination. From 17 osteometric type I landmarks, a dataset was built with five classic distances traditionally reported in the literature and six new distances selected using the two-step ratio method. A ten-fold cross-validation was performed, and a decision tree was established on two subsamples (training and test sets). The decision tree established on the training set included three nodes and its application to the test set correctly classified 92% of individuals. This percentage was similar to the data of the literature. The usefulness of decision trees has been demonstrated in numerous fields. They have been already used in sex determination, body mass prediction, and ancestry estimation. This study shows another use of decision trees enabling simple and accurate sex determination.     

Postcranial Sex Estimation Criteria for Mexican Hispanics

Population-specific reference data are necessary for sex estimation in forensic anthropological practice. Currently, there are no population-specific data for Hispanics equivalent to data available for American Blacks and Whites. Individuals of Mexican origin represent the largest group of Hispanics in the United States (Spradley and Jantz. 2011. J Forensic Sci;56:289). This paper presents new population-specific sex estimation criteria for postcranial measurements for Mexican Hispanics. Metric data come from positively identified border-crossing fatalities at the Pima County Office of the Medical Examiner and documented cemetery collections curated at Universidad Nacional Autónoma de México and Universidad Autónoma de Yucatán. Stepwise variable selection procedures and discriminant function analyses were utilized to generate classification functions for postcrania. Sectioning points were also created for select measurements. Both the cross-validated classification rates and sectioning points achieved accuracy rates as high as 95% and 92%, respectively. These new criteria will improve sex estimation for US Mexico border crossers and Hispanics in the US.     

Improving Sex Estimation from Crania Using a Novel Three‐dimensional Quantitative Method,,

This study utilizes an innovative 3D approach to discover metric variables that obtain the highest classification rates for sex estimation from the cranium. Models were constructed from 222 cranial CT scans of U.S. Whites from the Bass Donated Collection. These models were used to create a statistical bone atlas that captures the primary shape variation in the skull and facilitates rapid computer‐automated analyses. The bone atlas showed that important size‐related sex variables are bizygomatic breadth, maximum cranial length, cranial base length, and mastoid height. Shape‐related variables capture sex differences in the projection of the glabellar region, inclination of the frontal, and cranial base flexion. In addition, vault thickness is highly dimorphic, with females having on average thicker vaults in the frontal region, and males having thicker vaults in the occipital region. Cross‐validated linear discriminant analysis obtained >95% accuracy (97.5% with 11 variables and 95.5% with eight variables).     

Mastoid Triangle for Sex Determination in Adult Nigerian Population: A Validation Study

In the quest for a simple, reliable technique to estimate the sex of human remains several novel metric skeletal indices have been reported. Only a few have been examined for utility in populations different from those in which they were developed. In this study, the mastoid process was evaluated for sex determination using 102 lateral cephalograms of a Nigerian sample of known age and sex. The asterion‐mastoidale distance and mastoid triangular area were sexually dimorphic with mean values higher in males compared with females (p = 0.02). On analysis of the discriminant function, overall accuracy for sex classification was 55%. On cross‐validation, the triangular area accurately identified 80% of females and 48% of males. The asterion‐mastoidale distance was slightly more accurate at sexing the sample. The practical utility of the mastoid triangle area technique to differentiate sex in Nigerian populations is not supported by the results of this study.     

Adapting and Applying the Phenice (1969) Adult Morphological Sex Estimation Technique to Subadults

This research evaluated whether adult morphological sex estimation methods of the innominate could be adapted and applied to subadults. The subpubic concavity, described by Phenice (1969) and revised by Klales et al. (2012), was modified for use with subadults. Two observers scored radiographic images from the PATRICIA database of 334 individuals of both sexes aged between 1.19 and 20.47 years. Score frequencies shifted from score 2 (straight) to higher frequencies of score 3 (convexity) in males and score 1 (concavity) in females with increasing age. Using ordinal logistic regression, sex classification was highest for the oldest age cohort at 97.2% and then decreased by age cohort. Interobserver error rendered a high level of agreement (0.806) using the intraclass correlation coefficient. Results indicate that the Klales method can be modified and applied to subadults to accurately estimate sex following the onset of puberty with a high degree of reliability and validity.     

Development and Assessment of Postcranial Sex Estimation Methods for a Guatemalan Population

This study tests whether postcranial sex estimation methods generated from Hispanic, and mainly Mexican samples, can be successfully applied to other increasingly common migrant populations from Central America. We use a sample of postcranial data from a modern (1980s) Guatemalan Maya sample (n = 219). Results indicate a decrease in classification accuracies for previously established univariate methods when applied to the Guatemalan study sample, specifically for males whose accuracies ranged from 30 to 84%. This bias toward inaccuracies for Guatemalan males is associated with the smaller skeletal sizes for the Guatemalan sample as compared to the samples used in the tested sex estimation methods. In contrast, the tested multivariate discriminant function classification yielded less sex bias and improved classification accuracies ranging from 82 to 89%. Our results highlight which of the tested univariate and multivariate methods reach acceptable levels for accuracy for sex estimation of cases where the region of origin may include Guatemala.     

Sex Estimation from Human Cranium: Forensic and Anthropological Interest of Maxillary Sinus Volumes

Sex estimation is a key objective of forensic science. We aimed to establish whether maxillary sinus volumes (MSV) could assist in estimating an individual's sex. One hundred and three CT scans were included. MSV were determined using three‐dimensional reconstructions. Two observers performed three‐dimensional MSV reconstructions using the same methods. Intra‐ and interobserver reproducibility were statistically compared using the intraclass correlation coefficient (ICC) (α = 5%). Both intra‐ and interobserver reproducibility were perfect regarding MSV; both ICCs were 100%. There were no significant differences between right and left MSV (p = 0.083). No correlation was found between age and MSV (p > 0.05). We demonstrated the existence of sexual dimorphism in MSV (p < 0.001) and showed that MSV measurements gave a 68% rate of correct allocations to sex group. MSV measurements could be useful to support sex estimation in forensic medicine.     

Sex Determination from the Frontal Bone: A Geometric Morphometric Study

Sex estimation in human skeletal remains when using the cranium through traditional methods is a fundamental pillar in human identification; however, it may be possible to incur in a margin of error due because of the state of preservation in incomplete or fragmented remains. The aim of this investigation was sex estimation through the geometric morphometric analysis of the frontal bone. The sample employed 60 lateral radiographs of adult subjects of both sexes (30 males and 30 females), aged between 18 and 40 years, with mean age for males of 28 ± 4 and 30 ± 6 years for females. Thin‐plate splines evidenced strong expansion of the glabellar region in males and contraction in females. No significant differences were found between sexes with respect to size. The findings suggest differences in shape and size in the glabellar region, besides reaffirming the use of geometric morphometrics as a quantitative method in sex estimation.     

Sexual Dimorphism in Finger Ridge Breadth Measurements: A Tool for Sex Estimation from Fingerprints

Previous research has demonstrated significant sexual dimorphism in friction ridge skin characteristics. This study uses a novel method for measuring sexual dimorphism in finger ridge breadths to evaluate its utility as a sex estimation method from an unknown fingerprint. Beginning and ending in a valley, the width of ten parallel ridges with no obstructions or minutia was measured in a sample of 250 males and females (N = 500). The results demonstrate statistically significant differences in ridge breadth between males and females (p < 0.001), with classification accuracy for each digit varying from 83.2% to 89.3%. Classification accuracy for the pooled finger samples was 83.9% for the right hand and 86.2% for the left hand, which is applicable for cases where the digit number cannot be determined. Weight, stature, and to a lesser degree body mass index also significantly correlate with ridge breadth and account for the degree of overlap between males and females.     

Distal Humerus Morphological Variation and Sex Estimation in Modern Thai Individuals,

Due to differential preservation, it is necessary to develop sex estimation methods on varied anatomical regions, including the distal humerus. Sexually dimorphic differences of the medial epicondyle angle, olecranon fossa shape, trochlear extension, and trochlear constriction have been documented in several non-Asian groups. This study examines distal humerus morphological variation in 616 modern Thai individuals (f = 198; m = 418) 18–96 years old and tests the methods on a hold-out sample of 152 individuals (f = 91; m = 61). The results indicate that population-specific binary probit regression performs the best (74.1–100%), followed by composite scoring (77.0–90.1%), binary logistic regression (63.3–92.2%), and univariate sectioning points (37.7–90.1%). Age minimally effects the expression of the medial epicondyle angle in males, and trait scoring is susceptible to high intra- and interobserver error. While demonstrating relatively high sex biases, distal humerus morphology can be used to estimate the sex of Thai individuals when more sexually dimorphic regions are absent.     

The Influence of Body Size on the Expression of Sexually Dimorphic Morphological Traits

Skeletal sexual dimorphism manifests as size or shape differences between males and females in a population. Certain dimorphic traits are used in sex estimation methods, and populational variation in the expression of these traits can result in inaccurate sex estimation. However, the underlying causes of variation in trait expression remain unclear. This study explores body size, which also exhibits sexual dimorphism, as a potential factor influencing trait expression. To test this, skeletons of 209 individuals of varying body size were analyzed, and morphological traits were scored according to the Walker (2008), Klales et al. (2012), and Rogers (1999) sex estimation methods. Statistical analyses found significant correlations between body size parameters and expression of traits, with stature explaining more relative variance in trait expression than body mass. However, the relationships are weak and few in number, suggesting that body size has a minimal impact on the expression of these morphological traits.     

A Test of Sex Estimation in Subadults Using the Elevation of the Auricular Surface from Four Samples of Known Age and Sex

Biological sex is foundational to the work of forensic anthropologists and bioarcheologists. The lack of reliable biological sex estimation methods for subadults has, thus, greatly limited forensic and bioarcheological analyses. Auricular surface elevation showed promise as a subadult sex estimation method in previous studies. This study examined two auricular surface elevation evaluation methods on four subadult samples of known age, sex, and ancestry. Samples were scored as “male,” “female,” or “indeterminate” and results were examined with chi‐square analysis. No consistent sex estimation pattern, accuracy, or predictive value was produced between samples. Only one test was significant using Fisher's exact test analysis (FET = 7.501, p < 0.022): the composite approach on the Hamann‐Todd sample. While age, sample size, or developmental factors may play a role in these results, clearly sample variation does as well. This study found auricular surface elevation was not a useful subadult sex estimation method.     

Quantifying Sexual Dimorphism in the Human Cranium: A Preliminary Analysis of a Novel Method

In forensic anthropology, sexually dimorphic cranial features are traditionally visually assessed and scored using an ordinal scale, which is highly subjective. This study quantifies six cranial features using original three‐dimensional coordinate measurements to provide greater accuracy in sex estimation. Cranial features include supraorbital ridges, glabella, external occipital protuberance, nuchal protuberances, mastoid processes, and frontal bosses. Measurements were taken using coordinate calipers from 158 White and Black male and female crania from the Maxwell Documented Collection at University of New Mexico and Tennessee's Bass Collection. Overall, 72.2% of the crania were correctly classified. Males were correctly classified 69.9% of the time, while females were correctly classified 74.7% of the time. The overall value is similar to the results from traditional methods and suggests this method may be just as reliable as established visual sex estimation techniques.     

Secular Change in Morphological Pelvic Traits used for Sex Estimation

This research evaluates secular change in Phenice's (Am J Phys Anthropol, 30, 1969 and 297) three morphological traits of the pubis, as described by Klales et al. (Am J Phys Anthropol, 149, 2012 and 104): medial aspect of the ischio‐pubic ramus, subpubic contour, and ventral arc. Ordinal scores were collected for these traits and compared between a sample of innominates from the historical Hamann–Todd Collection (n = 170) and modern Bass Donated Collection (n = 129). Using the Freeman–Halton test, significant differences between temporal sample score frequencies were found for all traits in females and for the subpubic contour and ventral arc in males. Despite these findings, classification accuracy using logistic regression between the temporal periods remained low (68.7%). These results suggest that secular changes in trait expression are occurring; however, sex estimation methods using these traits and created with historical samples are still applicable to modern forensic cases. In fact, the secular changes occurring in these traits contribute to better classification accuracy between sexes in modern populations.     

Improving Nonmetric Sex Classification for Hispanic Individuals

Current techniques used by forensic anthropologists for the identification of unknown human skeletal remains have largely been created using U.S. Black and White samples. When applied to Hispanics, these techniques perform poorly and can lead to misclassifications; consequently, there is an imperative need for population‐specific standards for Hispanics. This research examines the classification accuracies obtained by the original Walker (Am J Phys Anthropol, 136, 2008) and Klales et al. (Am J Phys Anthropol, 149, 2012) methods for nonmetric sex estimation and provides recalibrated regression equations specifically for Hispanics. Ordinal data were collected for five skull and three pelvic traits from a sample of 54 modern Hispanic individuals. Recalibration of the Klales et al. equation improved accuracy (90.3% vs. 94.1%), while recalibration of the Walker method equation decreased accuracy (81.5% vs. 74.1%), but greatly improved sex bias (22.2% vs. ?7.4%), thereby making the recalibrated equations more appropriate for use with Hispanics.