The Impact of Racial Metric Variation in the Os Coxae on the Morphological Assessment of Sex*

Abstract: This study examines whether sex determination based on morphological traits in the os coxae is impacted by racial quantitative variation. Nineteen traits were evaluated independently by two observers in 876 os coxae. Chi‐square test was used on a random sample of 400 individuals to assess whether the distribution of correct sex assessment varied for white and black individuals based on each trait individually and all 19 traits collectively, as well as on inter‐observer agreement in correct sex assessment. Results indicate that accuracy of sex assessment varied between white and black individuals in certain individual traits; however, accuracy was not impacted when all traits were considered together. Furthermore, traits that showed significant variation in correct sex assessment between races generally were not related to size, but instead were “discrete.” Finally, analyses of inter‐observer variation suggest that disparities in sex assessment for some traits may be related to differences in trait interpretation between observers rather than morphological dissimilarities between races.     

Application of Fordisc 3.0 to Explore Differences Among Crania of North American and South African Blacks and Whites,

Using discriminant function analysis, classification accuracies for ancestry and sex in white and black South Africans were compared using North American (FDB), African groups in Howells (HDB), and South African (SADB) databases in FORDISC 3.0. (FD3). Twenty‐four standard linear measures were collected from a total of 86 black and 101 white crania obtained from the Pretoria Bone Collection. White and black South Africans classified 73% correctly in FDB, 55% correctly in HDB, and 71% correctly in SADB. The percentage of atypical cases was higher with FDB than SADB. In all three databases, misclassification occurred more with sex than ancestry revealing differences in sexual dimorphism between population groups. Broad ancestral differences may explain low misclassification rates for ancestry. FD3, with a modern South African reference sample, can assist South African anthropologists to standardize methodology and to justify procedures for estimating ancestry.     

Evaluating the accuracy and precision of cranial morphological traits for sex determination

Sex determination is a key analysis that forensic anthropologists perform in order to construct a biological profile of human remains. The techniques used in forensic investigations must meet the Mohan or Daubert criteria, for admissibility in a court of law. In this study, the precision and accuracy of 21 morphological characteristics of the skull were tested on a modern sample of 50 adult crania of European White ancestry. The following craniofacial features are identified as high-quality traits, defined by intraobserver error or=80%: mastoid size, supraorbital ridge size, general size and architecture, rugosity of the zygomatic extension, size and shape of the nasal aperture, and gonial angle. Ninety-six percent accuracy and 92% precision were achieved using 20 traits in combination. Fisher's exact probability tests revealed no significant differences (p=0.05) in the levels of precision or accuracy between age categories. Sex-related bias in accuracy was found for the following cranial features: ramus symphysis (p=0.009), zygomatic extension (p=0.0016), and occipital markings (p=0.0013). These traits demonstrated a greater tendency to be scored male than female.     

The Optimized Summed Scored Attributes Method for the Classification of U.S. Blacks and Whites: A Validation Study

Recently, Hefner and Ousley (2014) introduced the optimized summed scored attributes (OSSA) method that maximizes between‐group differences in U.S. black and white populations by dichotomizing six cranial morphoscopic trait scores. This study tests OSSA using an independent skeletal sample (Hamann‐Todd, n = 208) and positively identified forensic cases (Mercyhurst University, n = 28, and New York City Office of Chief Medical Examiner, n = 38). An evaluation of trait frequencies suggests shifting the heuristically selected sectioning point separating U.S. black and white populations from ≤ 3 to ≤ 4. We found a total correct classification of 73.0% (B = 50.9%, W = 89.2%) using the originally suggested sectioning point of ≤3, while the total correct classification increases to 79.2% (B = 80.2%, W = 78.5%) with a modified sectioning point of ≤4. With the increased total correct classification and reduced classification bias between ancestry groups, we suggest the modified sectioning point of ≤4 be used when assessing ancestry in forensic unknowns.     

Further evidence to show population specificity of discriminant function equations for sex determination using the talus of South African blacks

Several studies have shown that osteometric differences exist between different population groups. Thus, discriminant function equations derived for the determination of sex from skeletal elements are population specific. In a previous study, the authors derived such equations from nine measurements of the talus of South African whites with high levels of average accuracies. The validity of some of the equations was tested on data collected from a South African black sample that consisted of 120 tali, equally distributed by sex, derived from the Raymond A. Dart Collection of Human Skeletons. The average accuracies dropped significantly. This necessitated the derivation of new equations for the South African black population and the average accuracies obtained ranged between 80% and 89%. The validity of the equations derived from the present study was tested using the leave-one-out classification and two independent samples (1 and 2). The applicability of the equations with very high classification rate from the present study was tested on Independent sample 1 of 10 white tali with poor results. The result of the validity of these equations on an Independent sample 2 of 10 black tali revealed acceptably high average accuracies in correct classification thereby supporting earlier observations on population specificity of discriminant function equations.     

Nonmetric sex determination from the distal and posterior humerus in black and white South Africans

The successful identification of human skeletal remains relies on proven diagnostic techniques for sex determination. This research utilized 608 individuals from South Africa (420 men, 188 women) to conduct a blind nonmetric determination of sex from three features of the distal humerus: olecranon fossa shape, angle of the medial epicondyle, and trochlear extension. A scoring system between males and females was implemented, and the aggregate score of the three features determined the estimated sex of the skeletal element in question. With all features combined, black and white South Africans were categorized successfully as either male or female 75.5% (77% accuracy rate for females, 74% accuracy rate for males). This classification rate is lower than what was found in previous studies, but suggests that characteristics of the distal humerus are still quite valuable when estimating skeletal sex. More research is needed to assess reasons for the differential expression of these traits in different populations and to determine whether the method is nonpopulation specific.     

Forensic Applicability of Femur Subtrochanteric Shape to Ancestry Assessment in Thai and White American Males

Ancestry assessment from the postcranial skeleton presents a significant challenge to forensic anthropologists. However, metric dimensions of the femur subtrochanteric region are believed to distinguish between individuals of Asian and non‐Asian descent. This study tests the discriminatory power of subtrochanteric shape using modern samples of 128 Thai and 77 White American males. Results indicate that the samples' platymeric index distributions are significantly different (p ≤ 0.001), with the Thai platymeric index range generally lower and the White American range generally higher. While the application of ancestry assessment methods developed from Native American subtrochanteric data results in low correct classification rates for the Thai sample (50.8–57.8%), adapting these methods to the current samples leads to better classification. The Thai data may be more useful in forensic analysis than previously published subtrochanteric data derived from Native American samples. Adapting methods to include appropriate geographic and contemporaneous populations increases the accuracy of femur subtrochanteric ancestry methods.     

An evaluation of non-metric cranial traits used to estimate ancestry in a South African sample

Establishing ancestry from a skeleton for forensic purposes has been shown to be difficult. The purpose of this paper is to address the application of thirteen non-metric traits to estimate ancestry in three South African groups, namely White, Black and "Coloured". In doing so, the frequency distribution of thirteen non-metric traits among South Africans are presented; the relationship of these non-metric traits with ancestry, sex, age at death are evaluated; and Kappa statistics are utilized to assess the inter and intra-rater reliability. Crania of 520 known individuals were obtained from four skeletal samples in South Africa: the Pretoria Bone Collection, the Raymond A. Dart Collection, the Kirsten Collection and the Student Bone Collection from the University of the Free State. Average age at death was 51, with an age range between 18 and 90. Thirteen commonly used non-metric traits from the face and jaw were scored; definition and illustrations were taken from Hefner, Bass and Hauser and De Stephano. Frequency distributions, ordinal regression and Cohen's Kappa statistics were performed as a means to assess population variation and repeatability. Frequency distributions were highly variable among South Africans. Twelve of the 13 variables had a statistically significant relationship with ancestry. Sex significantly affected only one variable, inter-orbital breadth, and age at death affected two (anterior nasal spine and alveolar prognathism). The interaction of ancestry and sex independently affected three variables (nasal bone contour, nasal breadth, and interorbital breadth). Seven traits had moderate to excellent repeatability, while poor scoring consistency was noted for six variables. Difficulties in repeating several of the trait scores may require either a need for refinement of the definitions, or these character states may not adequately describe the observable morphology in the population. The application of the traditional experience-based approach for estimating ancestry in forensic case work is problematic.     

Application of the Optimized Summed Scored Attributes Method to Sex Estimation in Asian Crania

The optimized summed scored attributes (OSSA) method was recently introduced and validated for nonmetric ancestry estimation between American Black and White individuals. The method proceeds by scoring, dichotomizing, and subsequently summing ordinal morphoscopic trait scores to maximize between‐group differences. This study tests the applicability of the OSSA method for sex estimation using five cranial traits given the methodological similarities between classifying sex and ancestry. A large sample of documented crania from Japan and Thailand (n = 744 males, 320 females) are used to develop a heuristically selected OSSA sectioning point of ≤1 separating males and females. This sectioning point is validated using a holdout sample of Japanese, Thai, and Filipino (n = 178 males, 82 females) individuals. The results indicate a general correct classification rate of 82% using all five traits, and 81% when excluding the mental eminence. Designating an OSSA score of 2 as indeterminate is recommended.     

Radiographic Identification Using Midline Medical Sternotomy Wires,

Forensic anthropologists are regularly asked to assist with the identification of unknown individuals using comparative medical radiography. This study addressed the use of midline medical sternotomy wires as a means for personal identification. Antemortem and postmortem radiographic comparisons were completed by 46 professional forensic anthropologists and anthropology graduate students familiar with comparative medical radiography as a technique for assessing identification. Participants were asked to make five radiographic matches from a pool of 20 radiographs. Participants also completed an anonymous survey detailing their education level and experience making radiographic comparisons. Participants were 99.5% accurate in matching the radiographs. Sensitivity was 98.7%, and specificity was 99.7%. Logistic regression analysis found no statistically significant differences in the participants' ability to make a correct match. As the high accuracy rates indicate, the shape, size, and various characteristics of the sternotomy wires are individualizing and can confidently be used when assisting with personal identification cases.     

Evaluation of the (hu)MANid program for sex and ancestry estimation in a diverse,contemporary CT scan-based sample

Human remains from forensic and bioarcheological contexts are often fragmentary, requiring methods for estimating a forensic profile that are based upon limited skeletal features. In 2017, Berg and Keryhercz created an online application, (hu)MANid, that provides sex and ancestry estimation from mandibular morphoscopic traits and linear measurements. In this study, we examine the utility of the (hu)MANid application in a diverse, urban US adult sample (aged 20–45; n = 143) derived from computed tomography (CT) scans. We secondarily conduct a preliminary analysis of the program's utility in a sample of adolescents (aged 15–17; n = 40). Six morphoscopic, and eleven morphometric traits were recorded as directed by the literature associated with the (hu)MANid program. Percent correct classification and posterior predictive values were calculated for the sex and ancestry estimations output by the program; chi-squared tests were employed to compare self-reported and predicted ancestry. In the adult sample, sex was accurately predicted for 75.52% of the sample. Ancestry prediction, however, was less favorable ranging from 19.3% to 50% correct. For the adolescent sample, correct sex estimation (45%) did not surpass what could occur by chance alone, though ancestry prediction fared better than in the larger adult sample (percent correct prediction overall average: 47.5%, range 35.71%–71.43%). The (hu)MANid application shows utility for use with CT scan-derived adult samples for sex estimation, but caution is warranted for ancestry estimation and use with samples that may not have reached full adult maturity.     

Nasal aperture shape evaluation between black and white South Africans

The purpose of this study was to combine morphoscopic and metric analyses to assess variation in nasal aperture size and shape of black and white South Africans. Thirteen landmarks were digitized from the bony nasal region of 152 crania using an electromechanic instrument for geometric morphometric (general procrustes analysis) and craniometric analyses. Elliptical Fourier analysis was used to assess shape of the nasal aperture via outlines applied through photographs. Both principal component and discriminant function analyses were applied to these statistical methods. Black South Africans were classified 95-96% correctly and white South Africans were classified 91-94% correctly. In a four-way analysis of sex and ancestry, classification accuracy ranged from 56 to 70%. Most misclassifications were between the sexes within each group which suggests an absence of sexual dimorphism. This study found that there is quantifiable variation in shape of the nasal aperture between black and white South African groups using all three statistical methods. In forensic application, standard craniometrics can be used to accurately classify an unknown person.     

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.     

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.     

Quantification of the subpubic angle in South Africans

Due to the high crime rate in South Africa, forensic anthropologists are increasingly approached to aid in the identification of skeletonized remains, with sex and population affinity assignment being some of the most critical tasks they face. For over a century, the pelvis has been known to be one of the most sexually dimorphic bones of the human body and the subpubic angle is one of the most accurate, albeit scarcely quantified, features thereof. Hence, the aim of this study was to quantify the size of the subpubic angle and compare it between male and female South Africans of African (black) and European (white) descent. One hundred and forty five (145) pelves were selected, consisting of 68 white (43 male and 25 female) and 77 black South Africans (44 male and 33 female), from the Raymond A. Dart Collection of Human Skeletons housed at the University of the Witwatersrand, Johannesburg, South Africa. Each of the pelves were articulated and placed into a custom built stand for photographing. Measures of the subpubic angle from these digital images were subjected to numerous statistical analyses. Results indicated that significant differences exist between the sexes, as well as between the two population groups. For black individuals it was found that males generally possessed a subpubic angle of 74.9° or less, with larger values being indicative of the female sex. For white individuals, subpubic angles of 81.4° and less indicated males whilst larger values indicated females, with an average accuracy of 86% for both population groups. These results illustrate the advantages of using the subpubic angle to assist in the estimation of sex and population affinity and also reinforce the need for population specific parameters to be applied.     

Morphoscopic Trait Expression in “Hispanic” Populations

This study evaluates population variation of eight cranial morphoscopic traits using samples of known southwest Hispanics (n = 72), Guatemalans (n = 106), American Blacks (n = 146), and American Whites (n = 218). We applied the support vector machine (SVM) method to build a prediction model based on a subsample (20%) of the data; the remainder of the data was used as a test sample. The SVM approach effectively differentiated between the four groups with correct classification rates between 72% (Guatemalan group) and 94% (American Black group). However, when the Guatemalan and southwest Hispanic samples were pooled, the same model correctly classified all groups with a higher degree of accuracy (American Black = 96%; American White = 77%; and the pooled Hispanic sample = 91%). This study also identified significant differences between the two Hispanic groups in six of the eight traits using univariate statistical tests. These results speak to the unique population histories of these samples and the current use of the term “Hispanic” within forensic anthropology. Finally, we argue that the SVM can be used as a classification model for ancestry estimation in a forensic context and as a diagnostic tool may broaden the application of morphoscopic trait data for the assessment of ancestry.     

The configuration of cervical spinous processes in black and white South African skeletal samples

The present study investigates the frequency of bifidity/nonbifidity in the black and white South African populations. Four-hundred skeletons of known race, sex, and tribal group were examined. Spinous processes were classified as bifid (bifurcate and cleft subtypes) and nonbifid (obtuse, pediculate, acinate, and clavate subtypes). Statistical analysis using the chi-squared probability test (p < 0.05) was carried out. Bifid spinous processes were present significantly more frequently in the white sample (58.9%) than in the black (31.6%). A bifid spinous process occurred most commonly in C2 (89%) followed by C5 (83%), C4 (79%), C3 (59.4%), and C6 (41.7%) in the white sample. A similar order of decrease in bifidity occurred in the black sample. C2 most commonly displayed the bifurcate subtype of spinous process, while the clavate subtype of nonbifid spinous process was the most common in both populations. The significantly higher frequency of bifidity in the white South African sample when compared to the black sample may suggest a population difference.