Evaluating the Accuracy of Cranial Indices in Ancestry Estimation Among South African Groups

Historically, population differences were quantified using cranial indices. Even though the application of indices is associated with numerous statistical and methodological problems, the use of cranial indices to estimate ancestry persists as demonstrated by its inclusion in several recent papers and conference presentations. The purpose of this study was to classify 207 South African crania and compare the results of five standard cranial indices to linear discriminant analysis (LDA). New sectioning points were created to contend with low classification accuracies (40–79%) and possible secular trends. Although the accuracies of the new sectioning points increased (66–87%), the accuracies associated with the stepwise LDA were higher (84%) and could classify the crania into one of the three South African groups. The results of the study demonstrate that indices cannot compete with multivariate techniques and should not be used in forensic anthropological analyses for ancestry estimation.     

Do century-specific equations provide better estimates of stature? A test of the 19-20th century boundary for the stature estimation feature in Fordisc 3.0

A sample (n=28) from the Terry Collection was selected to include only White males who were born and had their entire growth and development period before 1900 to assess the effects year of birth have on accuracy and precision when estimating stature. Using the computer application Fordisc 3.0, stature was estimated using the humerus, radius, femur, and tibia equations developed from White males born in the 19th Century and the 20th Century. The 19th Century White male equations did not consistently provide the most precise and accurate estimates of stature. The 20th Century equations provide results that were as good as or slightly better than the 19th Century equations for the humerus, radius and femur. The 20th Century equations provided notably better results for the tibia. There is a great deal of evidence that there are clear positive secular changes in most of North America in the last 100-125 years, but the division commonly advocated in a forensic context at the year 1900 has no positive effect on accuracy or precision when estimating stature.     

Allocation of crania to groups via the "new morphometry".

An investigation regarding the variation in cranial morphology between American blacks and whites was conducted using triangulation schemes of inter-landmark distances and converting these to three dimensional coordinate data. A least squares superimposition method and Euclidean distance analysis were utilized to obtain parameters for classifying individuals in our sample, consisting of 19 black and nineteen white crania from the William M. Bass, III Donated and Forensic collections curated at the University of Tennessee, Knoxville. Thirty-six caliper measurements were collected on each skull based on 14 homologous cranial landmarks (nasion, bregma, lambda, prosthion, subspinale, basion, frontomalare (left and right), zygoorbitale (left and right), zygotemporale (left and right), and left and right asterion). The results are compared to traditional discriminant analysis. The classification results using the new morphometry are comparable to traditional discriminant analysis. However, the new morphometry can provide information as to the specific location of morphological variation that cannot be obtained with discriminant analysis.     

Fatal non-accidental pediatric cranial fracture risk and three-layered cranial architecture development

This study examines the influence of three-layered cranial architecture development upon blunt force trauma (BFT) cranial outcomes associated with pediatric non-accidental injury (NAI). Macroscopic and microscopic metric and morphological comparisons of subadult crania ranging from perinatal to 17 years of age chronicle the ontogenetic development and spatial and temporal variability in the emergence of a mature cranial architecture. Cranial vault thickness increases with subadult age, accelerating in the first 2 years of life due to rapid brain growth during this period. Three-layer differentiation of the cranial tables and diploë initiates by 3–6 months but is not consistently observed until 18 months to 2 years; diploë formation is not well developed until after age 4 and does not manifest a mature appearance until after age 8. These results allow topographic documentation of cortical and diploic development and temporal and spatial variability across the growing cranium. The lateral cranial vault is identified as expressing delayed development and reduced expression of the three-layer architecture, a pattern that continues into adulthood. Comparison of fracture locations from known BFT pediatric cases with identified cranial fracture high-risk impact regions shows a concordance and suggests the presence of a higher fracture risk associated with non-accidental BFT in the lateral vault region in subadults below the age of 2. The absence or lesser development of a three-layered architecture in subadults leaves their cranial bones, particularly in the lateral vault, thin and vulnerable to the effects of BFT.     

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.     

Biological sex variation in bone mineral density in the cranium and femur

Objectives

Sex and age trends in bone mineral density (BMD) play an important role in the estimation of age-at-death (AAD) of unidentified human remains. Current methodologies lack the ability to precisely estimate age in older individuals. In this study, BMD of the cranium and femur measured by DXA were examined to establish their applicability for age estimation in older adults. BMD as measured by DXA, is most commonly used clinically for prediction of osteoporotic fracture risk. We hypothesized that weight-bearing and non-weight-bearing bones, the femur and cranium, respectively, would provide valuable insights for aging.

A Test of a Recently Devised Method of Estimating Skeletal Age at Death using Features of the Adult Acetabulum

Estimation of age at death from adult skeletal remains is highly problematic, due in great part to interpopulation variability in skeletal age changes. Thorough testing of aging methods is therefore of key importance. A method recently devised by Calce (Am J Phys Anthropol 148 (2012): 11–23) for placing adult skeletons into three broad age at death classes (17–39, 40–64, 65+ years) on the basis of acetabular morphology is tested on a collection of 18–19th century AD skeletons (N = 185) of documented age at death from London. Results showed that 45% were correctly assigned to age class using this method. This compares with 81% reported by Calce on 20th century North American material. This indicates significant interpopulation differences in the relationship between the Calce acetabular variables and age, even between populations of European ancestry. Until the sources of this variation are better understood, caution should be used before applying this method to estimate age in unknown skeletons.     

Ancestry Estimation Using Cranial and Postcranial Macromorphoscopic Traits

Ancestry estimation methods using macromorphoscopic (MMS) traits commonly focus exclusively on cranial morphology. The objective of this study was to demonstrate the value of postcranial MMS traits, highlighting a combined cranial/postcranial trait approach to ancestry estimation using quadratic discriminant function and a variety of machine learning classification models including artificial neural networks (aNN), random forest models, and support vector machine. Eight cranial and eleven postcranial MMS traits were collected from the Terry and Bass Skeletal Collections (American Black = 81; American White = 173). Our classification models using cranial and postcranial traits correctly classified 88–92% of the sample, improving classification accuracies by nearly fifteen percent over models relying exclusively on cranial data. These same results demonstrate the importance of a multivariate statistical framework incorporating cranial and postcranial data and the nearly unlimited potential of machine learning models to improve the accuracy of ancestry estimates over traditional methods of analysis. To facilitate implementation in casework, one of the more robust models (aNN) is incorporated into a web-based application, ComboMaMD Analytical, to facilitate cranial and postcranial MMS traits analysis for ancestry estimation.     

Pitfalls of Computed Tomography 3D Reconstruction Models in Cranial Nonmetric Analysis*

Many studies in the literature have highlighted the utility of virtual 3D databanks as a substitute for real skeletal collections and the important application of radiological records in personal identification. However, none have investigated the accuracy of virtual material compared to skeletal remains in nonmetric variant analysis using 3D models. The present study investigates the accuracy of 20 computed tomography (CT) 3D reconstruction models compared to the real crania, focusing on the quality of the reproduction of the real crania and the possibility to detect 29 dental/cranial morphological variations in 3D images. An interobserver analysis was performed to evaluate trait identification, number, position, and shape. Results demonstrate a false bone loss in 3D models in some cranial regions, specifically the maxillary and occipital bones in 85% and 20% of the samples. Additional analyses revealed several difficulties in the detection of cranial nonmetric traits in 3D models, resulting in incorrect identification in circa 70% of the traits. In particular, pitfalls included the detection of erroneous position, error in presence/absence rates, in number, and in shape. The lowest percentages of correct evaluations were found in traits localized in the lateral side of the cranium and for the infraorbital suture, mastoid foramen, and crenulation. The present study highlights important pitfalls in CT scan when compared with the real crania for nonmetric analysis. This may have crucial consequences in cases where 3D databanks are used as a source of reference population data for nonmetric traits and pathologies and during bone-CT comparisons for identification purposes.     

Implications of dimorphism, population variation, and secular change in estimating population affinity in the Iberian Peninsula

Morphometric cranial variation among Spanish samples was compared to a 19th century Portuguese sample using both traditional and three-dimensional approaches. The Spanish samples included the regional 19th century Oloriz collection and the local 16-17th century Villanubla and Vallolid sample from northwestern Spain. Results suggest moderate variation among the samples and suggest that varying patterns of regional variation, sexual dimorphism and secular change represent important factors to be considered in the evaluation of population affinity using craniometric approaches.     

Sexual dimorphism in human browridge volume measured from 3D models of dry crania: A new digital morphometrics approach

Sex estimation from the human skull is often a necessary step when constructing a biological profile from unidentified human remains. Traditional methods for determining the sex of a skull require observers to rank the expression of sexually dimorphic skeletal traits by subjectively assessing their qualitative differences. One of these traits is the prominence of the glabellar region above the browridge. In this paper, the volume of the browridge region was measured from digital 3D models of 128 dry crania (65 female, 63 male). The 3D models were created with a desktop laser scanner, and the browridge region of each 3D model was isolated using geometric planes defined by cranial landmarks. Statistical analysis of browridge-to-cranium volume ratios revealed significant differences between male and female crania. Differences were also observed between geographically distinct populations, and between temporally distinct populations from the same locale. The results suggest that in the future, sex determination of human crania may be assisted by quantitative computer-based volume calculations from 3D models, which can provide increased objectivity and repeatability when compared to traditional forensic techniques. The method presented in this paper can easily be extended to other volumetric regions of the human cranium.     

Sexual dimorphism in the crania and mandibles of South African whites

Numerous studies have clearly demonstrated that skeletal characteristics vary by population. To date, there are no metric cranial criteria for South African whites. Therefore, the purpose of this study is to establish population specific standards for sex determination from the skull. A total of 12 standard cranial and five mandibular measurements were taken from 44 male and 47 female skeletons of known sex and race from the Pretoria and Dart collections. These were subjected to SPSS discriminant function analysis. Bizygomatic breadth was the most dimorphic dimension. Five functions were developed from the complete cranium, vault, face, mandible and bizygomatic breadth. Dimensions from the complete cranium provided the best accuracy. In the mandible, bigonial breadth was the most dimorphic of the measurements taken. Average accuracies ranged from 80% (bizygomatic breadth alone) to 86% (cranium). These accuracies are similar to those obtained by researchers on other groups (e.g., 84% in Japanese crania and about 86% in American whites and blacks). Diagnostic accuracy, however, is lower than that obtained from the South African femur and tibia.     

Blunt force cranial trauma in the Cambodian killing fields

In this paper we present a unique pattern of blunt force cranial trauma that was observed in 10 of a sample of 85 crania from a Cambodian skeletal collection comprised of Khmer Rouge victims. Initial examination of the trauma, which presents as substantial damage to the occipital with fractures extending to the cranial base, suggested the pattern was classifiable as a basilar or ring fracture. However, further investigation, including trauma analysis and historical research, revealed that this fracture type is distinctive from basilar and ring fractures. Historical data indicate that a particular execution method was the likely source of the trauma. Recognition of this trauma pattern is significant because it exemplifies the distinct fracture configuration resulting from an apparently categorical and methodical execution technique. Identification of this fracture type could potentially assist forensic investigators in the recognition of specific methods of murder or execution.     

Biparietal Thinning: Accidental Death by a Fall from Standing Height

Biparietal thinning resulting in bilateral and symmetrical resorption and loss of thickness of the parietal bones is an uncommon to rare condition in the anthropological and clinical literature. This enigmatic condition of unknown etiology was first reported in the 18th century and has been variously described as a nonmetric trait, anatomical variant, anomaly, and pathology. Biparietal thinning presents grossly and radiographically as oval‐shaped depressions in 0.25–0.8% and 0.4–0.5% of individuals and with a higher frequency in females over the age of 60 years. A review of the literature revealed only one example of cranial trauma associated with biparietal thinning and none of fatal trauma associated with this condition. This case reports a rare example of fatal trauma in an elderly man that resulted from a backward fall from a standing height and highlights the increased risk of craniocerebral trauma in individuals with this condition.     

The Cohort-Size Sample-Size Conundrum: An Empirical Analysis and Assessment Using Homicide Arrest Data from 1960 to 1999

A number of studies use the Age-Period-Cohort Characteristic (APCC) model to address the impact of cohort related factors on the age distribution of homicide offending. Several of these studies treat birth cohorts as spanning several years, an operationalization that most closely matches tenets of cohort theory, yet sharply reduces the number of observations available for analysis. Other studies define birth cohorts as those born within a single year, an operationalization that is theoretically problematic, but provides many more observations for analysis. We address the sample size problem by applying a time-series-cross-section model (panel model) with age-period-specific homicide arrest data from the United States for each year from 1960 to 1999, while operationalizing cohorts as five-year birth cohorts. Our panel model produces results that are very similar to those obtained from traditional multiyear APCC models. Substantively, the results provide a replication of work showing the importance of relative cohort size and cohort variations in family structure for explaining variations in age-period-specific homicide rates. The additional observations provided by our approach allow us to examine these relationships over time, and we find substantively important changes. The year-by-year estimates of the age distribution of homicide offending help us to examine the model during the epidemic of youth homicide.     

Demographic change and forensic identification: problems in metric identification of Hispanic skeletons

The United States (U.S.) population structure is currently in a state of flux with one of the most profound changes being the increasing number of people referred to as Hispanic. In the U.S., much of the identification criteria for a biological profile are based on American Black and White individuals from anatomical collections. Using metric data from the Forensic Anthropology Data Bank (FDB), this paper will attempt to explore several issues that forensic anthropologists face when confronted with Hispanic remains. These will involve estimation of sex, height, and ancestry, the initial components of a biological profile. Discriminant function analyses indicate that American White criteria provide poor estimations of sex when applied to Hispanics and that ancestry estimation of Hispanic crania is difficult. Additionally, a new linear regression equation is presented that estimates stature for Hispanic individuals, although population specific criteria are still needed for Hispanic individuals from diverse geographical origins.     

A Bayesian Approach to Age Estimation in Modern Americans from the Clavicle*

Abstract: Clavicles from 1289 individuals from cohorts spanning the 20th century were scored with two scoring systems. Transition analysis and Bayesian statistics were used to obtain robust age ranges that are less sensitive to the effects of age mimicry and developmental outliers than age ranges obtained using a percentile approach. Observer error tests showed that a simple three‐phase scoring system proved the least subjective, while retaining accuracy levels. Additionally, significant sexual dimorphism was detected in the onset of fusion, with women commencing fusion at least a year earlier than men (women transition to fusion at approximately 15 years of age and men at 16 years). Significant secular trends were apparent in the onset of skeletal maturation, with modern Americans transitioning to fusion approximately 4 years earlier than early 20th century Americans and 3.5 years earlier than Korean War era Americans. These results underscore the importance of using modern standards to estimate age in modern individuals.     

A Validation Study of the Langley et al. (2017) Decision Tree Model for Sex Estimation

Langley et al. (2017) developed a sex estimation decision tree utilizing two traditional cranial traits (glabella and mastoid) and a new trait: zygomatic extension. This study aimed to test the reliability of their zygomatic extension scoring method and validate their sex estimation method. Ordinal score data were collected from 281 male and female U.S. White and Black individuals. The five traditional cranial traits were collected from physical specimens, while zygomatic extension was scored from 3D cranial models. Intra‐ and interobserver analyses carried out on a subsample of 30 individuals indicate good agreement between zygomatic scores. The decision tree correctly sexed 71.5% of the sample, but a strong sex bias (94.2% correct for females, 49.3% correct for males) severely limits the utility of this method. The Walker (2008) and Stevenson et al. (2009) methods produced higher accuracy rates (80.8% and 82.6%, respectively), although these methods also produced sex and ancestry biases.     

Generating a Vertebrae‐based Method to Discriminate between Korean and U.S. White Male Casualties from the Korean War,

Low recovery rate of intact crania in conflict‐related contexts necessitates the use of postcranial elements for ancestry estimation. This study aimed to develop a new method to discriminate between Korean and U.S. White casualties from the Korean War using vertebrae. Maximum body heights of C2 through L5 were measured from 75 Korean and 51 U.S. males to generate discriminant functions. U.S. vertebral heights were statistically greater than Koreans in 18 out of 23 vertebrae (C2, C4‐6, T3‐6, and T8‐L5). The functions with lumbar vertebrae tended to yield higher correct classification ratios (CCR) than those with cervical or thoracic vertebrae. Inclusion of the femur and tibia lengths in the vertebrae‐involved functions enhanced the CCR's. Discriminant functions using the femur and tibia length were also presented. The results of this study are expected to complement the current practices of the Defense POW/MIA Accounting Agency and the Ministry of National Defense Agency for KIA Recovery and Identification, which are primarily based on cranial and dental morphology.